Luminaire device

ABSTRACT

An optical device for collecting light and selectively outputting or concentrating the light. A layer has an optical index of referaction n 1 , and top, bottom and side surfaces defining an angel of inclination φ. A back surface spans the top, bottom and side surface. A first layer is coupled to the bottom surface of the layer and has an index of refraction n 2 . The first layer index n 2  causes light input through the back surface of the layer to be preferentially output into the first layer. A second layer is coupled to the bottom of the first layer and selectively causes output of light into ambient. Additional layers, such as alight polarization layer, a polarization converting layer and a post LCD diffuser layer can be used to make preferential use of polarized light of diffuse light having passed through the LCD layer to enhance viewing of the output light

[0001] The present invention is concerned generally with a luminairedevice for providing selected light illumination. More particularly, theinvention is concerned with luminaires, such as a wedge, forbacklighting by light output from a liquid crystal display layer andalso by manipulating light polarization, recycling light of selectedpolarization and filtering selected light polarizations to enhance lightillumination and image output.

[0002] A variety of applications exist for luminaire devices, such as,for liquid crystal displays. For flat panel liquid crystal displays, itis important to provide adequate backlighting while maintaining acompact lighting source. It is known to use wedge shaped optical devicesfor general illumination purposes. Light is input to such devices at thelarger end; and light is then internally reflected off the wedgesurfaces until the critical angle of the reflecting interface isreached, after which light is output from the wedge device. Suchdevices, however, have only been used to generally deliver anuncollimated lighting output and often have undesirable spatial andangular output distributions. For example, some of these devices usewhite painted layers as diffuse reflectors to generate uncollimatedoutput light.

[0003] It is therefore an object of the invention to provide an improvedoptical device and method of manufacture.

[0004] It is another object of the invention to provide a novel threedimensional luminaire.

[0005] It is a further object of the invention to provide an improvedmultilayer tapered luminaire for optical purposes, such as forcontrolled utilization of light polarization.

[0006] It is still another object of the invention to provide a noveltapered luminaire device for controlled transmission or concentration oflight.

[0007] It is an additional object of the invention to provide a noveloptical device for providing collimated polarized light illuminationfrom the device.

[0008] It is yet a further object of the invention to provide animproved tapered luminaire having a polarization filter layer.

[0009] It is still another object of the invention to provide a novelluminaire allowing conversion of polarized light to enhance illuminationoutput from the invention.

[0010] It is yet a further object of the invention to provide animproved illumination system wherein a combination of a polarizationfilter layer and a light redirecting layer are utilized to provideimproved light illumination over a controlled angular range of output tothe viewer.

[0011] It is still a further object of the invention to provide a novelluminaire optical device wherein a combination of a polarization filter,polarization converting layer and a post LCD diffuser layer are used toenhance light illumination from the optical device.

[0012] It is yet a further object of the invention to provide animproved luminaire optical device wherein an LCD layer is disposedadjacent an overlying post LCD diffuser layer to enable control of lightdistribution over broader angles to viewers without loss of light outputor image qualities.

[0013] It is also another object of the invention to provide an improvedluminaire optical device having an internal polarization cavity forconverting luminaire light to one polarization state for enhancedillumination gain.

[0014] It is yet an additional object of the invention to provide anovel luminaire optical device having a selected arrangement of astructured back reflector layer with a polarization beam splitter toenhance illumination efficiency.

[0015] It is still another object of the invention to provide animproved luminaire optical device having a polarization converting layerinteracting with a structural back reflector layer to provide enhancedillumination efficiency.

[0016] It is also a further object of the invention to provide a novelluminaire optical device having a polarization beam splitter, a quarterwave converting layer and a microstructural back reflector layer toprovide enhanced illumination gain.

[0017] It is yet another object of the invention to provide an improvedluminaire optical device having a selectable arrangements ofpolarization splitting layers including one of (a) the splitting layerevaporated directly onto a base layer of the luminaire, and (b)evaporation of the splitting layer onto a separate glass plate.

[0018] It is also an additional object of the invention to provide anovel luminaire optical device including a quarter plate polarizationconverting element in one of a set of selectable arrangements of (a)disposed between a back reflector and luminaire base layer with airlayers between, (b) coupled directly to a back reflector with an airlayer between the luminaire base layer and the directly coupled layers,(c) coupled directly to the luminaire base layer with an air layerbetween the converting element and a metallic back reflector layer or aBEF type of back reflector, (d) coupled directly to the luminaire baselayer on one side and a high efficiency mirror on the other side, and(e) coupled directly to the luminaire base layer on one side thereof andan air layer and back reflector on the other side of the base layer.

[0019] It is yet a further object of the invention to provide animproved luminaire optical device having a textured base layer forenhancing illumination properties.

[0020] It is still another object of the invention to provide a novelluminaire optical device utilizing a film based reflective polarizer incombination with a converter layer and BEF type back reflector.

[0021] It is also a further object of the invention to provide animproved luminaire optical device having a base layer separated byvarious air layers with polarized splitter, redirecting, converter, andback reflector layers disposed above and/or below the base layer.

[0022] It is yet an additional object of the invention to provide anovel luminaire optical device including a back reflector below a baselayer and a redirecting layer adjacent the top surface of the base layerand a reflective polarizer and redirecting/diffuser layer positionedabove the redirecting layer.

[0023] Other objects, features and advantages of the present inventionwill be readily apparent from the following description of the preferredembodiments thereof, taken in conjunction with the accompanying drawingsdescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows a prior art wedge shaped device;

[0025]FIG. 2A illustrates a multilayer tapered luminaire deviceconstructed in accordance with the invention; FIG. 2B is a magnifiedpartial view of the junction of the wedge layer, the first layer and thesecond faceted layer; FIG. 2C is an exaggerated form of FIG. 2A showinga greatly enlarged second faceted layer; FIG. 2D is a partial view ofthe junction of the three layers illustrating the geometry forbrightness determinations; FIG. 2E is a multilayer wedge device with alight redirecting, internally transmitting layer on the bottom; FIG. 2Fshows a wedge device with a lower surface translucent layer; FIG. 2Gshows a wedge layer with a lower surface refracting faceted layer; FIG.2H shows a wedge layer with a lower surface refracting layer and curvedfacets thereon; FIG. 2I shows a wedge layer with a refracting layer offacets having variable facet angles; FIG. 2J shows a single refractingprism coupled to a wedge layer; FIG. 2K shows a single refracting prismcoupled to a wedge layer and with an integral lens; FIG. 2L shows areflecting faceted layer coupled to a wedge device; FIG. 2M shows areflecting faceted layer with curved facet angles and coupled to a wedgedevice; FIG. 2N shows a flat reflecting facet on a wedge layer and FIG.20 shows a curved reflecting facet on a wedge layer;

[0026]FIG. 3A illustrates a multilayer wedge device with curved facetson the ambient side of the second layer and FIG. 3B shows a magnifiedpartial view of the junction of the various layers of the device;

[0027]FIG. 4A shows calculated brightness performance over angle for anasymmetric range of angles of illumination; FIG. 4B shows calculatedbrightness distribution performance over angle for a more symmetricangle range; FIG. 4C illustrates calculated brightness performance overangle for the symmetry of FIG. 4B and adding an external diffuserelement; FIG. 4D illustrates an output using flat reflecting facets, noparallel diffuser; full-width at half-maximum brightness (FWHM=7degrees; FIG. 4E illustrates an example of nearly symmetrical outputdistribution, measured using flat facets with parallel lenticulardiffuser; FWHM=34 degrees; FIG. 4F illustrates an example ofasymmetrical output distribution, measured using curved facets; FWHM=32degrees; FIG. 4G illustrates an example asymmetrical outputdistribution, measured using curved facets; FWHM=26 degrees; FIG. 4Hillustrates an example of a bimodal output distribution, measured usingone faceted reflecting layer and one faceted refractive layer; and FIG.4I illustrates an example of an output distribution with large “tails”,measured using a diffuse reflective bottom redirecting layer and arefracting/internally reflecting top redirecting layer;

[0028]FIG. 5A shows a top view of a disc shaped light guide and FIG. 5Billustrates a cross section taken along 5B-5B in FIG. 5A;

[0029]FIG. 6A shows a cross sectional view of a multilayer taperedluminaire device with an air gap layer included; FIG. 6B shows anothertapered luminaire in cross section with a compound parabolic lightsource/concentrator; FIG. 6C illustrates another tapered luminaire incross section with a variable parametric profile light source and alenticular diffuser; and FIG. 6D shows another tapered luminaire incross section with non-monotonic wedge layer thickness;

[0030]FIG. 7 illustrates a reflective element disposed concentricallyabout a light source;

[0031]FIG. 8 illustrates a reflective element disposed about a lightsource with maximum displacement between the reflector center ofcurvature and the center of the light source;

[0032]FIG. 9A illustrates use of a redirecting layer to provide asubstantially similar angular distribution emanating from all portionsof the device and FIG. 9B illustrates use of a redirecting layer to varyangular distribution emanating from different portions of the device,and specifically to focus the various angular distributions to enhancetheir overlap at a selected target distance;

[0033]FIG. 10 illustrates one form of pair of lenticular arrays of aluminaire; and

[0034]FIG. 11 illustrates a lenticular diffuser array and curved facetlayer of a luminaire;

[0035]FIG. 12A illustrates a wedge shaped luminaire having a pair ofdiffraction gratings or hologram layers; FIG. 12B shows a wedge shapedluminaire with a pair of refracting facet layers and diffusers; FIG. 12Cillustrates a wedge shaped luminaire with a pair of faceted layers; FIG.12D shows a wedge shaped luminaire with two refracting single facetlayers; FIG. 12E illustrates a wedge shaped luminaire with a refractingsingle facet layer and a bottom surface redirecting layer; FIG. 12Fshows a luminaire with a top surface redirecting layer of a refractingfaceted layer and a bottom surface refracting and internally reflectinglayer; FIG. 12G illustrates a luminaire with a top surfacerefracting/internally reflecting faceted layer and a bottom surfacerefracting/internally reflecting faceted layer; FIG. 12H shows aluminaire with a top surface refracting faceted layer and a bottomsurface refracting/internally reflecting faceted layer; FIG. 121illustrates a luminaire with a bottom surface specular reflector and atop layer transmission diffraction grating or transmission hologram;FIG. 12J shows a luminaire with a bottom surface specular reflector anda top surface refracting faceted layer and diffuser; FIG. 12Killustrates a luminaire with a bottom layer specular reflector and a toplayer refracting/internally reflecting faceted layer; FIG. 12L shows aluminaire with a bottom specular reflector and a top layerrefracting/internally reflecting faceted layer, FIG. 12M illustrates aluminaire with an initial reflector section including an integrallenticular diffuser; FIG. 12N shows a luminaire with a roughened initialreflector section of a layer; FIG. 12O illustrates a luminaire with aneccentric light coupler and converging to the wedge shaped section; FIG.12P shows a luminaire with an eccentric light coupler and a diffuser androughened or lenticular reflector; FIG. 12Q illustrates a luminaire witha bottom specular or diffusely reflecting layer and a top refractinglayer and FIG. 12R shows a luminaire for generating a “bat wing” lightoutput;

[0036]FIG. 13 illustrates a combination of two wedge shaped sectionsformed integrally and using two light sources;

[0037]FIG. 14 shows a tapered disk luminaire including a facetedredirecting layer;

[0038]FIG. 15 illustrates a luminaire operating to provide a collimatedlight output distribution;

[0039]FIG. 16A shows a prior art ambient mode LCD and FIG. 16Billustrates a prior art transflective LCD unit;

[0040]FIG. 17 shows a luminaire operative in ambient and active modeswith a faceted redirecting layer and a lenticular diffuser;

[0041]FIG. 18A illustrates a luminaire with an array of microprisms fora faceted surface disposed over a diffuse backlight and with themicroprisms having equal angles on both sides, but each microprismhaving progressively changing facet angles across the face; FIG. 18Bshows a microprism array as in FIG. 18A with the sides of eachmicroprism having different angles varying again across the facetedsurface;

[0042]FIG. 19A illustrates a luminaire having a polarization filterlayer; FIG. 19B shows a luminaire with a plurality of layers including apolarization filter layer; and FIG. 19C shows a variation on FIG. 19Bwith layer indices enabling output of both polarizations of light on oneside of the luminaire;

[0043]FIG. 20A illustrates a luminaire similar to FIG. 19B but furtherincludes a reflector layer; FIG. 20B illustrates a luminaire as in FIG.20A but a redirecting layer is disposed on the same side of the baselayer and the polarization filter; and FIG. 20C is a variation on FIG.20B with an additional redirecting layer and rearrangedn₂/filter/redirecting layers;

[0044]FIG. 21A illustrates a luminaire having a polarization convertinglayer and polarization filter layer; FIG. 21B is a variation on FIG. 21Awith the polarization filter layer and polarization converting layer onthe same side of the base layer;

[0045]FIG. 22A illustrates a luminaire with a polarization filter layerone side of the base layer and a polarization converting layer on theother side; FIG. 22B shows a variation on FIG. 22A with the filter andconverting layers adjacent one another on the same side of the baselayer; FIG. 22C shows a further variation of FIGS. 22A and B and with areflector layer added; FIG. 22D illustrates a further variation on FIG.22C with the converting layer moved to the other side of the base layerand FIG. 22E shows another variation on FIG. 22D;

[0046]FIG. 23A illustrates a luminaire having plural layers including apolarization filter, a converting, a redirecting, a reflector and an LCDlayer; FIG. 23B shows a variation on FIG. 23A; and FIG. 23C illustratesyet another variation on FIG. 23A;

[0047]FIG. 24A illustrates a luminaire with two polarization filterlayers for two polarization states; FIG. 24B shows a variation on FIG.24A plus an added light redirecting layer; FIG. 24C is a furthervariation on FIG. 24B with a matching layer, a second redirecting layerand an LCD layer; FIG. 24D is yet another variation on FIGS. 24B and C;FIG. 24E is a variation on FIG. 24D with an-added converting layer andtwo polarization filter layers and two redirecting layers and FIG. 24Fis still another variation on FIG. 24E with LCD layers on both sides ofthe base layer;

[0048]FIG. 25A illustrates a general construction utilizing twopolarization filter layers and a polarization converting layer; FIG. 25Bshows a variation on FIG. 25A with an added redirecting layer;

[0049]FIG. 26A illustrates a multilayer luminaire with a light sourcecoupled to a light angle transformer to control spatial uniformity oflight output from the device; FIG. 26B is a variation on FIG. 26A;

[0050]FIG. 27A illustrates a luminaire with a faceted redirecting layerand light polarization and polarization converting layers; and FIG. 27Bis a variation on FIG. 27A, wherein the redirecting layers includes areflecting layer with curved facets for focusing light in a preferredviewing zone;

[0051]FIG. 28A illustrates a luminaire including a polarization lightfilter, polarization converter and a faceted redirecting and diffusinglayer; FIG. 28B shows a variation on FIG. 28A with two polarizationfilter layers and two faceted redirecting layer; FIG. 28C shows a lightsource coupled to a luminaire and is a variation on FIG. 28A; FIG. 28Dis a variation on FIG. 28C; and FIG. 28E is yet another variation onFIG. 28C;

[0052]FIG. 29A illustrates a luminaire with polarized light output incombination with an LCD layer and FIG. 29B is a variation on FIG. 29A;

[0053]FIG. 30A illustrates a conventional LCD display system; FIG. 30Bshows a polarization filter layer; FIG. 30C illustrates a multilayerthin film form of polarization filter; FIG. 30D shows a Brewster Stackform of polarization filter; FIG. 30E illustrates a birefringent plateand interacting polarized light; FIG. 30F shows Eulerian angles andoptical vectors; FIG. 30G shows a backlight providing collimated lightin the xz plane and FIG. 30H shows a detailed enlargement of a zone fromFIG. 30G;

[0054]FIG. 31A illustrates a luminaire with a coupled birefringentlayer; FIG. 31B shows a luminaire and birefringent layer and an addedlight redirecting layer; FIG. 31C illustrates a luminaire system similarto FIG. 31B with an added light polarization converting layer; FIG. 31Dis similar to FIG. 31C but the converting layer is on the same side ofthe base layer as the birefringent layer; FIG. 31E illustrates avariation on FIG. 31C with the converting layer coupled directly to thebase layer; FIG. 31F is similar to FIG. 31D but the redirecting layercomprises a faceted layer; FIG. 31G is based on the embodiment of FIG.3F but also includes a matching layer, an LCD layer and a diffuserlayer; and FIG. 31H is a variation on FIG. 31G;

[0055]FIG. 32A illustrates a luminaire system including an LCD layer anda post LCD diffuser layer for processing unpolarized light; FIG. 32B isa variation on FIG. 32A; and FIG. 32C is a variation on FIG. 32B;

[0056]FIG. 33 illustrates a luminaire system including a quarter waveconverting layer and BEF based type of back reflector below the baselayer and polarization splitter and redirecting layer above the baselayer;

[0057]FIG. 34 illustrates another form of FIG. 33 without the convertinglayer;

[0058]FIG. 35 illustrates a luminaire system including a BEF based typeof back reflector below the base layer and a light redirecting layerabove the base layer;

[0059]FIG. 36 illustrates another form of FIG. 33 substituting ametallic back reflector for the BEF based type of back reflector layer;

[0060]FIG. 37 illustrates another form of FIG. 36 except thepolarization splitting layer is directly disposed onto the base layer;

[0061]FIG. 38 illustrates another form of FIG. 35 except the backreflector layer is a metallic back reflector layer,

[0062]FIG. 39 illustrates another form of FIG. 36 except the quarterwave plate converting layer is laminated to the base layer;

[0063]FIG. 40 illustrates a luminaire system with a polarization cavityformed by the base layer and a laminated converting layer;

[0064]FIG. 41 illustrates another form of FIG. 40 but a polarizationsplitting layer is directly disposed onto the top surface of the baselayer;

[0065]FIG. 42 illustrates a variation on FIGS. 40 and 41 with a backreflector layer directly coupled to the converting layer laminated tothe bottom surface layer of the base layer;

[0066]FIG. 43 illustrates a luminaire system having a polarizationconverting layer disposed above the top surface of the base layer;

[0067]FIG. 44 illustrates a variation of FIG. 43 with the base layermade of a birefringent polarization converting material;

[0068]FIG. 45 illustrates a variation of FIG. 39 with the back reflectorlayer being a BEF type back reflector;

[0069]FIG. 46 illustrates a variation on FIG. 40 with the back reflectorlayer being a BEF type back reflector;

[0070]FIG. 47 illustrates a luminaire system having a polarizationsplitting layer disposed at the input to the base layer;

[0071]FIG. 48 illustrates a variation on FIG. 47 with a polarizationconverting layer on the lamp cavity side of the polarization splittinglayer;

[0072]FIG. 49 illustrates a variation on FIG. 33, not including aredirecting layer, the base layer being textured and a film basedreflective polarizer substituted for the interference layer;

[0073]FIG. 50 illustrates a variation on FIG. 49, not having thetextured base layer;

[0074]FIG. 51 illustrates a variation on FIG. 49 with the metallic backreflector substituted for the BEF type back reflector,

[0075]FIG. 52 illustrates a variation on FIG. 51 with the base layer notbeing textured;

[0076]FIG. 53 illustrates a variation on FIG. 33 with the reflectivepolarizer layer substituted for the interference layer and the baselayer is textured;

[0077]FIG. 54 illustrates a variation on FIG. 53 except the redirectinglayer is switched with the reflective polarizer layer;

[0078]FIG. 55 illustrates a variation on FIG. 53 with the convertinglayer positioned above the base layer;

[0079]FIG. 56 illustrates a variation on FIG. 53 with the convertinglayer laminated to the base layer;

[0080]FIG. 57 illustrates a variation on FIG. 35 using a textured formof the base layer;

[0081]FIG. 58 illustrates a polarized luminaire system operated withoutuse of a separate converter layer;

[0082]FIG. 59 illustrates a variation on FIG. 58 with the polarizerlayer positioned below the redirecting/diffuser layer;

[0083]FIG. 60 illustrates a variation on FIG. 53 with polarizationcreated by off-angle reflections;

[0084]FIG. 61A illustrates a top view of a luminaire output measurementsystem and a luminaire device; and 61B illustrates two half luminaires;

[0085]FIG. 62 illustrates a measured angle factor versus maximumbrightness; and

[0086]FIG. 63 illustrates typical vertical distributions from apolarized and unpolarized luminaire using a standard backlight and abacklight using a coated plate polarization beam splitter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0087] A multilayer luminaire device constructed in accordance with oneform of the invention is illustrated in FIG. 2 and indicated generallyat 10. A prior art wedge 11 is shown generally in FIG. 1. In this wedge11 the light rays within the wedge 11 reflect from the surfaces untilthe angle of incidence is less than the critical angle (sin⁻¹1/n) wheren is the index of refraction of the wedge 11. The light can exit equallyfrom both top and bottom surfaces of the wedge 11, as well as exiting atgrazing angles.

[0088] The multilayer luminaire device 10 (hereinafter “device 10”)shown in FIG. 2A includes a base or wedge layer 12 which has acharacteristic optical index of refraction of nil. The term “wedgelayer” shall be used herein to include all geometries having convergingtop and bottom surfaces with wedge shaped cross sectional areas. The x,y and z axes are indicated within FIGS. 2A and 2C with the “y” axisperpendicular to the paper. Typical useful materials for the wedge layer12 include almost any transparent material, such as glass, polymethylmethacrylate, polystyrene, polycarbonate, polyvinyl chloride, methylmethacrylate/styrene copolymer NAS) and styrene/acrylonitrile. The wedgelayer 12 in FIG. 2A further includes a top surface 14, a bottom surface16, side surfaces 18, edge 26 and a back surface 20 of thickness t_(o)spanning the top, bottom and side surfaces. A light source, such as atubular fluorescent light 22, injects light 24 through the back surface20 into the wedge layer 12. The light 24 is internally reflected fromthe various wedge layer surfaces and is directed along the wedge layer12 toward the edge 26. Other possible light sources can be used and willbe described hereinafter. Generally, conventional light sources providesubstantially incoherent, uncollimated light; but coherent, collimatedlight can also be processed by the inventions herein.

[0089] For the case where the surfaces 14 and 16 are flat, a singleangle of inclination φ for a linear wedge is defined by the top surface14 and the bottom surface 16. In the case of nonlinear wedges, acontinuum of angles φ are definable; and the nonlinear wedge can bedesigned to provide the desired control of light output orconcentration. Such a nonlinear wedge will be described in more detaillater.

[0090] In the embodiment of FIG. 2A a first layer 28 is coupled to thewedge layer 12 without any intervening air gap, and the first layer 28has an optical index of refraction n₂ and is optically coupled to thebottom surface 16. The first layer 28 can range in thickness from a fewlight wavelengths to much greater thicknesses and accomplish the desiredfunctionality. The resulting dielectric interface between the wedgelayer 12 and the first layer 28 has a higher critical angle than at theinterface between the wedge layer 12 and ambient. As will be apparenthereinafter, this feature can enable preferential angular output andcollimation of the light 24 from the device 10.

[0091] Coupled to the first layer 28 is a second layer 30 (best seen inFIG. 2B) having an optical index of refraction n₃ which is greater thann₂, and in some embodiments preferably greater than n₁. Thisconfiguration then allows the light 24 to leave the first layer 28 andenter the second layer 30. In the embodiment of FIG. 2A there aresubstantially no intervening air gaps between the first layer 28 and thesecond layer 30. In the preferred form of the invention illustrated inFIG. 2A, n₁ is about 1.5, n₂<1.5 and n₃ ≧n ₁. Most preferably, n₁=1.5,n₂<1.5 (such as about one) and n₃≧n₁.

[0092] In such a multilayer configuration for the device 10 shown inFIG. 2, the wedge layer 12 causes the angle of incidence for each cyclictime of reflection from the top surface 14 to decrease by the angle ofinclination 2φ (relative to the normal to the plane of the bottomsurface 16). When the angle of incidence with the bottom surface 16 isless than the critical angle characteristic of the interface between thewedge layer 12 and the first layer 28, the light 24 is coupled into thefirst layer 28. Therefore, the first layer 28 and the associated opticalinterface properties form an angular filter allowing the light 24 topass when the condition is satisfied: θ<θ_(c)=sin⁻¹ (n₂/n₁). That is,the described critical angle is higher than for the interface betweenair and the wedge layer 12. Therefore, if the two critical angles differby more than 6φ, nearly all of the light 24 will cross into theinterface between the wedge layer 12 and the first layer 28 before itcan exit the wedge layer 12 through the top surface 14. Consequently, ifthe two critical angles differ by less than φ, a substantial fraction,but less than half, of the light can exit the top surface 14. If the twoangles differ by more than φ and less than 6φ, then substantially morethan half but less than all the light will cross into the wedge layer 12and the first layer 28 before it can exit the wedge layer 12 through thetop surface 14. The device 10 can thus be constructed such that thecondition θ<θ_(c) is satisfied first for the bottom surface 16. Theescaping light 24 (light which has entered the layer 28) will then enterthe second layer 30 as long as n₃>n₂, for example. The light 24 thenbecomes a collimated light 25 in the second layer 30 provided by virtueof the first layer 28 being coupled to the wedge layer 12 and having theproper relationship between the indices of refraction.

[0093] In order to generate an output of the light 24 from the device10, the second layer 30 includes means for scattering light, such as apaint layer 33 shown in FIG. 2E or a faceted surface 34 shown in bothFIGS. 2B and 2C. The paint layer 33 can be used to preferentiallyproject an image or other visual information. The paint layer 33 cancomprise, for example, a controllable distribution of particles havingcharacteristic indices of refraction.

[0094] By appropriate choice, light can also be redirected back throughthe wedge layer 12 and into ambient (see light 29 in FIGS. 2A and 2C) oroutput directly into ambient from the second layer 30 (see light 29′ inFIG. 2F).

[0095] In other forms of the invention a further plurality of layerswith associated “n” values can exist. In one preferred form of theinvention the index of the lowest index layer can replace n₂ inequations for numerical aperture and output angle (to be providedhereinafter). Such further layers can, for example, be interveningbetween the wedge layer 12 and the first layer 28, intervening betweenthe first layer 28 and the second layer 30 or be overlayers of the wedgelayer 12 or the second layer 30.

[0096] In certain embodiments the preferred geometries result in outputof light into ambient without being reflected back through the wedgelayer 12. For example, in FIG. 2F the device 10 can include atranslucent layer 37. In another form of this embodiment shown in FIG.2G, a refracting layer 38 is shown. The refracting layer 38 can includeflat facets 39 for providing a collimated output. Also shown in phantomin FIG. 2G is a transverse lenticular diffuser 83 which will bedescribed in more detail hereinafter. The diffuser layer 83 can be usedwith any of the invention geometries, including above the wedge layer 12as in FIG. 6A.

[0097] In yet another example shown in FIG. 2H, the refracting layer 38can include curved facets 41 for providing a smoothly broadened outputover a desired angular distribution. In a further example shown in FIG.2I, the refracting layer 38 includes variable angle facets 42. Thesefacets 42 have facet angles and/or curvature which are varied withposition across the facet array to focus output light in a desiredmanner. Curved facets would enable producing a softly focused regionwithin which the entire viewing screen appears to be illuminated.Examples of the application to computer screen illumination will bedescribed hereinafter. In FIGS. 2J and 2K are shown, respectively, asingle refracting prism element 43 and the prism element 43 with anintegral lens 44 to focus the output light. FIGS. 2L and M show thefaceted surface 34 with the facets angularly disposed to control theoutput distribution of light. In FIGS. 2K and 2L the light is output toa focal point “F”, while in FIG. 2M the output is over an approximateviewing range 45. FIGS. 2N and 20 illustrate flat reflecting facets 48and curved reflecting facet 49 for providing a collimated light outputor focused light output, respectively.

[0098] As shown in FIGS. 2A and C the faceted surface 34 opticallyreflects and redirects light 29 through the second layer 30, the firstlayer 28 and then through the wedge layer 12 into ambient. Only afraction of each facet is illuminated, causing the output to appearalternately light and dark when viewed on a sufficiently small scale.Since this pattern is typically undesirable, for the preferredembodiment shown in FIG. 2B the period of spacing between each of thefaceted surfaces 34 is preferably large enough to avoid diffractioneffects, but small enough that the individual facets are not detected bythe intended observing means. The spacing is also chosen to avoidforming Moiré interference patterns with any features of the device tobe illuminated, such as a liquid crystal display or CCD (charge coupleddevice) arrays. Some irregularity in the spacing can mitigateundesirable diffraction Moiré effects. For typical backlightingdisplays, a spacing period of roughly 0.001-0.003 inches can accomplishthe desired purpose.

[0099] The faceted surface 34 in FIGS. 2B and 2C, for example, can begenerally prepared to control the angular range over which theredirected light 29 is output from the device 10. The minimumdistribution of output angle in the layer 30 has a width which isapproximately equal to:

Δθ=2φ[(n ₁ ² −n ₂ ²)/(n ₃ ² −n ₂ ²)]^(1/2)

[0100] Thus, since φ can be quite small, the device 10 can be quite aneffective collimator. Therefore, for the linear faceted surface 34, theexiting redirected light 29 has a minim um angular width in air ofapproximately:

Δθair=n ₃Δθ=2φ(n ₁ ² −n ₂ ²)/[1−(n ₂ /n ₃)²]^(1/2).

[0101] As described hereinbefore, and as shown in FIGS. 2H, 2I, 2K, 2L,2M, and FIG. 3, the facet geometry can be used to control angular outputin excess of the minimum angle and also focus and control the directionof the output light.

[0102] Fresnel reflections from the various interfaces can also broadenthe output angle beyond the values given above, but this effect can bereduced by applying an anti reflection coating 31 on one or more of theinternal interfaces, as shown in FIG. 2B.

[0103] The brightness ratio (“BR”) for the illustrated embodiment can bedetermined by reference to FIG. 2D as well as by etendue match, and BRcan be expressed as:${B.R.} = \frac{{output}\quad {brightness}}{{source}\quad {brightness}}$

[0104] or, B.R=illuminated area/total area

[0105] B.R.=[1−(n₂/n₃)²]^(1/2)=0.4−0.65 (for most transparent dielectricmaterials). For example, the wedge layer 12 can be acrylic (n₁=1.49),the first layer 28 can be a fluoropolymer (n₂=1.28-1.43) or Sol-gel(n₂=1.05-1.35, fluoride salts (n₂=1.38-1.43) or silicone based polymeror adhesive (n₂=1.4-1.45); and the second layer 30 can be a facetedreflector such as polycarbonate (n₃=1.59), polystyrene (n₃=1.59) epoxy(n₃=1.5-1.55) or acrylic (n₃=1.49) which have been metallized at the airinterface.

[0106] The flat, or linear, faceted surfaces 34 shown, for example, inFIGS. 2B and 2C can redirect the incident light 24 to control directionof light output and also substantially preserve the angular distributionof light Δθ which is coupled into the second layer 30 by theangle-filtering effect (see, for example, FIG. 4D). For example, in onepreferred embodiment shown in FIG. 2L, the faceted surfaces 34 reflectlight with the flat facet angles varied with position to focus theoutput light. In FIG. 2M the faceted surfaces 34 include curved facetangles which vary with position to produce a softly focused viewing zone45 within which the entire screen appears to be illuminated (see also,for example FIGS. 4F and 4G). Also show in phantom in FIG. 2M is anexemplary liquid crystal display 47 usable in conjunction with theinvention. As further shown in FIGS. 3A and B, curved facets 36 alsoredirect the incident light 24, but the facet curvature increases theresulting range of angular output for the redirected light 29 (see forcomparison for flat facets FIG. 2D). For example, it is known that aconcave trough can produce a real image, and that a convex trough canproduce a virtual image (see, for example, FIG. 3B). In each case theimage is equivalent to a line source emitting light uniformly over thedesired angular output range. Consequently, an array of such troughshaped facets 36 can redirect the incoming form of collimated light 25from the first layer 28 (see FIG. 2C), and a plurality of such linesource images then form the redirected light 29. By arranging thespacing of the curved facets 36 to less than human eye resolution, theresulting array of line sources will appear very uniform to an observer.As previously mentioned, the choice of about three hundred to fivehundred lines/inch or 0.002 to 0.003 inches for the period of facetspacing provides such a result. For a typical LCD display viewingdistances of approximately twenty inches or greater are conventional.

[0107] Other useful facet shapes can include, for example, parabolic,elliptical, hyperbolic, circular, exponential, polynomial polygonal, andcombinations thereof. The user can thus construct virtually arbitrarydistributions of averaged brightness of illumination using differentfacet designs. For example, polygon shaped facets can be used to produceoutput angular distributions having multiple peaks.

[0108] Examples of brightness distribution over various ranges ofangular output using a curved-faceted reflector are illustrated in FIGS.4A-4C, 4F and 4G. FIGS. 4C and 4E shows the brightness distribution inthe case of a reflector having linear facets, and further including adiffuser element 40 (shown in phantom in FIG. 2C). The predictedperformance output is shown for the various angular ranges (see FIGS.4A-4C) and compared with the measured angular output of light for acommercially available source (labeled “Wedge”), such as a “Wedge Light”unit, a trademark of Display Engineering. The preferred angular rangecan readily be modified to accommodate any particular viewing andcollimation requirements up to the minimum angle Δθ (air) describedhereinbefore by the equation in terms φ, n₁, n₂ and n₃. Thismodification can be accomplished by progressively changing the curvatureof the curved facets 36 in the manner shown in FIG. 2M and discussedhereinbefore. In addition to the illustrated control of the verticalviewing angular range, modification of the horizontal viewing range canalso be accomplished by appropriate changes of the shape of the curvedfacets 36. The above described angular distributions shown in FIGS.4A-41 are representative when the device 10 is processing the light 24within the numerical aperture NA=(n₁ ²−n₂ ²)^(1/2). When light isoutside this range, additional techniques can be applied to help controlthe angular output range.

[0109]FIGS. 9A and 9B further illustrate the use of redirecting means toprovide a tightly overlapping focused illumination output and a lessoverlapping focused illumination output, respectively. These conceptscan be applied practically by considering that a typical portablecomputer screen 87 has a vertical extent “V” of about 150 mm, while atypical viewing distance, “D”, is 500 mm. A viewer at distance “D”,positioned normal to the vertical center of the computer screen 87 willview different areas of the screen 87 at angles ranging from −8.5°measured at the top of the screen 87 to +8.5° measured at the bottom ofthe screen 87. This variation in viewing angle can, however, causeundesirable effects in use of a system having such screen illumination.Such a limited illumination angle for the screen 87 implies a limitedrange of positions from which a viewer can see a fully illuminatedscreen 87 (see FIG. 9A). Defining the viewer position in terms of theangle and distance from the center of the screen 87, then the effectiveangular range is substantially reduced below the nominal illuminationangle. For example, if the nominal illumination range is ±20° measuredat each individual facet, then the effective viewing range is reduced to±12° in the typical flat panel illuminator shown in FIG. 9A. Theresulting illumination between 12°-20°, either side of center for thescreen 87, will appear to be nonuniform to the viewer.

[0110] The invention herein can be used to overcome the above describednonuniformities by controlling the orientation of the faceted surface34. As illustrated, for example, in FIG. 2M both surfaces of the facetsare rotated progressively such that the flat facet surface is variedfrom 35.6° to 33.3° relative to, or parallel to, the edges of the planesdefining the various layers of the device 10. This systematic variationfrom the top to the bottom of screen 89 (see FIG. 9B) results in theredirected output illustrated. The faceted surface 34 can further becombined with the diffuser 83 and the like to produce a variable, butcontrollable light illumination output distribution. A flat facetedsurface 168 can further be combined with a diffuser 170. Therefore, asshown in FIG. 9B the ability to rotate the angular distributions oflight at different points on the screen 89 enable compensation for thevariation in viewing angle with position. Systematic variations in thefaceted surface 34 can further include variations in to focus the outputof any faceted redirecting layer. Examples are shown in FIGS. 2I and 2L.

[0111] In another example of overcoming nonuniformities of illumination,an array of micro-prisms for the faceted surface 34 can be laid over aconventional diffuse backlight 101 (see FIG. 18A). This faceted surface34 operates by a combination of refraction and total internal reflectionto permit only a limited angular range to be output through the layerinto ambient. This angular range depends on the facet angles. For thecase of acrylic film (n=1.49), highest brightness is typically achievedwith a prism included angle of 90-100 degrees, resulting in a viewingangle of approximately ±35 degrees. Backlights using such a geometryshow a sharp “curtaining” effect which is disconcerting to many viewers.This effect can be ameliorated by rotating the facets 38 from top tobottom of the screen to produce a focusing effect (see FIG. 18B). Simpleray-tracing shows that, for included angles in the range of 100°-110°, afacet rotated by an angle 3 will produce an angular distribution rotatedby approximately {fraction (3/2)}. In the embodiment shown in FIG. 18the progressive variation of facet face angle can vary asposition >along the faceted surface 34 wherein, for example:

Ψ₁=35°−(0.133°/mm)·x

Ψ₂=35°+(0.133°/mm)·x

[0112] This progressive facet angle change will produce an angulardistribution which varies by approximately ten degrees across the screen89, and satisfies the generic constraints outlined above.

[0113] Whatever the desired facet shapes, the faceted surface 34 (see,FIG. 2D) is preferably formed by a conventional process such as moldingor other known milling processes. Details of manufacture will bedescribed hereinafter.

[0114] Nonlinear Wedges.

[0115] In another form of the invention the wedge layer 12, which is theprimary lightguide, can be other than the linear shape assumedhereinbefore. These shapes allow achievement of a wide variety ofselected light distributions. Other shapes can be more generallydescribed in terms of the thickness of the wedge layer 12 as a functionof the wedge axis “Z” shown in FIGS. 2B and C (the coordinate axis whichruns from the light input edge to the small or sharp edge 26). For thelinear shaped wedge,

A(z)=A_(o) −C·z  (1)

A_(o) maximum wedge thickness (see FIG. 2A)

C=constant=tan φ

[0116] A large range of desired spatial and angular distributions can beachieved for the light output power (power coupled to the second layer30). This light output power is thus the light available for output tothe ambient by the appropriately faceted surfaces 34 or 36, or even bythe diffuse reflector 33 (see FIG. 2E) or other means.

[0117] For example, if L and M are direction cosines along the x and yaxes, respectively, then L_(o) and M_(o) are the values of L and M atthe thick edge (z=0). This initial distribution is Lambertian withinsome well-defined angular range, with little or no light outside thatrange. This distribution is especially important because idealnon-imaging optical elements have limited Lambertian outputdistributions. The key relationship is the adiabatic invariant, A(z)cos(θ_(c)) which is approximately equal to A₀L₀ and which implicitly givesthe position (z) of escape. To illustrate this concept, suppose wedesire uniform irradiance so that dP/dz=constant. Suppose fiber that theinitial phase space uniformly fills an elliptical area described by thefollowing expression:

L _(o) ²/σ² +M ₀ ²/τ²=1  (2)

[0118] where τ is the dimension of an ellipse along the M axis and σ isthe dimension of the ellipse along the L axis.

[0119] Then, dP/dL=const·[1−L²/σ²]^(1/2) but dA/dz=[A_(o)/L_(c)]dL_(o)/dZ where L_(c)=cos θ_(c). Therefore,[1−(L_(c)A)²/(A_(o)σ)²]^(1/2) dA=constant times dz. Suppose σ=L_(c) inthe preferred embodiment. This result can be interpreted by thesubstitution A/A₀=sin u, so that A=A₀ sin u and u+½ sin(2u)=(π/2)(1−z/D) where D is the length of the wedge layer 12.

[0120] If the desired power per unit length is dP/dz, more generally,then the desired shape of the wedge layer 12 is determined by thedifferential equation: $\begin{matrix}{{{{A(z)}}/{z}} = {- \frac{{P}/{{z\left( {A_{o}/\left\lbrack {1 - \left( {n_{2}/n_{1}} \right)^{2}} \right\rbrack^{1/2}} \right)}}}{{P}/{L_{o}}}}} & (3)\end{matrix}$

[0121] Note that in all these cases the output distribution has onlyapproximately the desired form because it is modified by Fresnelreflections. Note also that even when the wedge device 10 is curved, ifthe curvature is not too large, it may still be useful to define anaverage angle φ which qualitatively characterizes the system.

[0122] In another aspect of the invention the geometry of the aboveexamples has an x,y interface between two refractive media with indicesn₁ and n_(2a). The components nM,nN are conserved across the interfaceso that n₁M₁=n₂M₂, n₁N₁=n₂M₂. The angle of incidence projected in thex,z plane is given by sin θ_(eff)=N/(L²−N²)^(1/2). Then using the aboverelations, sin θ_(2eff)/sin θ_(1 eff)=(n₁/n₂)[1−M₁²]^(1/2)/[1−(n₁/n₂)²M₁ ²]^(1/2)=(n₁/n₂)_(eff). For example, for n₁=1.49,n₂=1.35, M₁=0.5, the effective index ratio is 1.035(n₁/n₂), which isonly slightly larger than the actual index ratio.

[0123] Variation of Index of Refraction Over Spatial Parameters.

[0124] In the general case of tapered light guides, the wedge layer 12is generally along the z axis with the narrow dimension along the x axis(see, for example, FIG. 2A). If we introduce optical direction cosines(nL,nM,nM) where L,M,N are geometric direction cosines along x,y,z, thenn is the refractive index which may vary with spatial position. Forguided rays in the wedge layer 12, the motion in x is almost periodic,and the quantity φnLdx for one period is almost constant as the raypropagates along z. This property is called adiabatic invariance andprovides a useful framework for analyzing the lightguide properties.

[0125] In a first example the wedge device 10 shown in FIG. 2A has auniform index in the wedge layer 12 and is linearly tapered in z withwidth A(z)=A₀−C·z. Then, along the zigzag ray path, L(z)A(z) isapproximately equal to a constant by adiabatic invariance. If a raystarts at z=0 with L=L₀, then (A₀−C·z)L(z) is approximately equal toL₀A₀. The ray will leak out of the wedge layer 12 when L=cos θ_(c) whereθ_(c) is the critical angle=[1−(n₂/n₁)²]^(1/2). Thus, the condition forleaving the wedge layer 12 is A₀−C·z=L₀A₀/cos θ_(c). This will occur atz=(A₀/C)(1−l₀/cos θ_(c)). Consequently, the density of rays emerging inz is proportional to the density of rays in the initial direction cosineL₀. For example, the density will be uniform if the initial distributionin L₀ is uniform.

[0126] In a second example, the index profile is no longer uniform butfalls off both in x and in z. If the fall-off in z is much slower thanin x, the light ray path is still almost periodic, and the aboveadiabatic invariance still applies. Then, as the light ray 24 propagatesin z, the path in x,nL space is almost periodic. Therefore the maximumvalue of L(z) increases and at some z may reach the critical value forescape. The z value for escape depends on the details of the index (n)profile. When this is specified, the analysis proceeds as in example oneabove. Thus, for a parabolic index profile, the index profile has theform n²(x)=n₂ ⁰[1−2Δ (x/ρ)²] for −ρ<xρ, =n₁ ²=n₂ ⁰[1−2Δ] for |x|>ρ.Then, the critical angle at x=0 is still given by sin²θ_(c)=2Δ=1−(n₁/n₀)². Then, if we have n₀ a slowly decreasing function ofz, the slope θ at x=0 will slowly increase by the adiabatic invarianceof φnLdx, while θ_(c) decreases so that light rays will escape. Thedetails of the light ray distributions will depend on how the index (n)varies with z.

[0127] Nonwedge Tapered Geometries

[0128] In the most general case the light can be input into any shapelayer (e.g., parallelepiped, cylinder or non-uniform wedge), and theprinciples described herein apply in the same manner, In addition, theindex of refraction can be varied as desired in (x,y,z) to achieve theappropriate end result when coupled to means to output light to ambient.

[0129] For example, consider a disc-shaped light guide 46 which istapered in the radial direction r shown in FIG. 5. The direction cosinesin cylindrical polar coordinates are k_(r), k_(θ), k_(z). Light 48propagating in this guide 46 satisfies the relationship:

φnk_(z)dz˜constant. (adiabatic invariance)  (4)

nrk_(θ)=constant. (angular momentum conservation)   (5)

[0130] The adiabatic invariance condition is identical with that for thewedge device 10, and the previous discussions pertinent to the wedgedevice 10 also thus apply to the light guide 46. The angular momentumconservation condition requires that as the light streams outward fromsource 47 with increasing radius, the k₇₄ value decreases. Therefore,the light becomes collimated in the increasing radial direction. Thismakes the properties fundamentally like the wedge device 10, and thelight 48 can be made to emerge as light 52 at a selected angle to face51, collimated along the z direction.

[0131] For purposes of illustration we take the guide material to have aconstant index of refraction n. For such geometries the light rays 48along the two-dimensional cross sectional plane taken along 5B-5B behavejust as in the case of the wedge device 10 counterpart describedhereinbefore. Similarly, various additional layers 54 and 56 and othermeans can be used to achieve the desired light handling features. Forexample, for the disc light guide 46 a preferred facet array 56 is aseries of circles, concentric with the disk 46. Thus, if the facets 56are linear in cross section, the light rays 52 will emerge in adirection collimated within a full angle of 2 φtimes a function of theindices of refraction as in the device 10 described hereinbefore.

[0132] Tapered Luminaires with Two Low-index Layers.

[0133] In another form of the invention shown in FIG. 6A, the device 10includes a first layer 61 having an optical index of refraction n₁ and afirst or top layer surface 62 and a second or bottom layer surface 64converging to establish at least one angle of inclination φ. The firstlayer 61 also includes a back surface 65 spanning the top layer surface62 and the bottom layer surface 64.

[0134] Adjacent the first layer 61 is layer means, such as a bottomtransparent layer means, like a first intermediate layer 66 of index n₂disposed adjacent to, or underlying, the bottom layer surface 64. Inaddition, the layer means can embody a top transparent layer means,second intermediate layer 81 of index n₂ disposed adjacent to the toplayer surface 62. At least one of the layers 66 and 81 can be an airgap, or other gas or a transparent dielectric gap.

[0135] An air gap can be established by conventional means, such as byexternal supports, such as suspending the layers under tension (notshown) or by positioning spacers 68 between the first layer 61 and theadjacent light redirecting layer 70. Likewise, the spacers 68 can bepositioned between the first layer 61 and the second light redirectinglayer 82. Alternatively, solid materials can be used for the transparentdielectric to constitute layers 66 and 81 and can improve structuralintegrity, robustness and ease of assembly. Such solid materials caninclude, for example, sol-gels (n₂=1.05-1.35), fluoropolymers(n₂=1.28-1.43), fluoride salts (n₂=1.38-1.43), or silicone-basedpolymers and adhesives (n₂=1.40-1.45). Such solid materials for thetransparent dielectric need no separate means to support or maintain it,but can result in lower N.A. acceptance since the index is higher thanfor an air gap.

[0136] The layers 66 and 81 allow transmission of light received fromthe first layer 61. In this embodiment part of the light will achieveθ_(c) first relative to the top layer surface 62, and light will enterthe layer 81 for further processing by the light redirecting layer 82.The remaining light will thereby achieve θ_(c) first relative to thebottom layer surface 64, thus entering the layer 66 for furtherprocessing by the light redirecting layer 70.

[0137] In one preferred form of the invention (see FIG. 6A) both thelayers 66 and 81 are present and can have similar, but significantlydifferent indices n_(2a) and n_(2b), respectively. The indices areconsidered similar when they establish critical angles at the interfaces62 and 64 which are similar in magnitude to the wedge angle φ, forexample:

|arcsin (n_(2a)/n₁)−arcsin (n_(2b)/n₁)|<6φ  (6)

[0138] In this case significant, but unequal, fractions of light willenter each of the layers 66 and 81 for further processing by redirectinglayers 70 and 82, respectively. The larger fraction will enter the layerhaving the higher of the two indices n_(2a) and n_(2b). The redirectinglayer 70 processes only the fraction which enters the layer 66.Therefore, the influence of the redirecting layer 70 on the outputangular distribution of light can be changed by varying the relationshipbetween the indices n_(2a) and n_(2b).

[0139] In another preferred form of the invention the layers 66 and 81can be the same transparent material of index n₂<n₁. In general, lowervalues of n₂ will enhance the efficiency of the device 10 by increasingthe numerical aperture at the light input surface 65. Therefore,collection efficiency can be maximized when the layers 66 and 81 aregaps filled with air or other gases (with n₂=1-1.01).

[0140] The thickness of the layers 66 and 81 can be selectively variedto control the output power spatial distribution of the device 10 or toenhance its visual uniformity. For example, increasing the thickness ofthe layer 81 by 0.002″-0.030″ sharply reduces non-uniformities whichtend to appear at the thicker end of the device 10. The thickness oflayers 66 and 81 can also be smoothly varied with position to influencea desired spatial distribution of the light being output (see FIG. 12L).

[0141] In one preferred form of the invention shown in FIG. 6A, thelight redirecting layer 70 includes a reflective layer 71 which reflectsthe light back through the layer 66 and the first layer 61. The light isthen output into the first layer 61 through the top layer surface 62,and ultimately through the light redirecting layer 82 for furtherprocessing. The reflective layer 71 can, for example, be any combinationof a planar specular reflector, a partially or completely diffusesreflector, or a faceted reflector.

[0142] Use of a planar specular reflector leads to the narrowest angulardistribution within the layer 81. Therefore, the reflector can simplifydesign of the light redirecting layer 82 when the desired output angulardistribution is unimodal. Diffuse or faceted reflectors can also be usedfor the layer 71 in order to achieve a large range of angulardistributions (see FIGS. 4H and I) or to increase uniformity (see FIG.4N). Diffuse reflectors are preferred if the desired angulardistribution has large “tails” (see, in particular, FIG. 41). Facetedreflectors can produce a bimodal angular distribution within the layer81 (see FIG. 4H). Therefore, such faceted reflectors are preferred ifthe desired output angular distribution is bimodal. For example, abimodal “batwing” distribution is preferred from luminaires for roomillumination because it reduces glare.

[0143] In general each facet of the layer 71 can be shaped to controlthe angular distribution of the light reflected back through the layer66 and the first layer 61 for further processing by the redirectinglayer 82. The angular distribution within the device 10 will in turninfluence the angular distribution of the light output into ambient fromthe redirecting layer 82. For example, curved facets can be used tosmoothly broaden the angular distribution, as well as providing adiffusing effect to improve uniformity. The reflective layer 71 can alsoinfluence the output power spatial distribution as well as the angulardistribution. The reflectivity, specularity, or geometry of thereflective layer 71 can be varied with position to achieve a desiredoutput distribution. For example, as described hereinbefore, smallvariations in the slope (see FIG. 12L) of each element of the reflectivelayer 71 as a function of position significantly change the light outputdistribution.

[0144] The light redirecting layer 82 has an index n₃>n₂, and issubstantially transparent or translucent. The light in the low-indexlayer 81 enters the layer 82 and is redirected into ambient. Thetransmissive redirecting layer 82 also redirects the light which hasbeen processed by reflection from the redirecting layer 71 thentransmitted back through the low-index layer 66 and the first layer 61.The transparency or geometry of the layer 82 can be varied with positionto further influence the output spatial distribution of the device 10.In one preferred form of the invention the redirecting layer 82 includesa faceted surface at the interface with the low-index layer 81, as shownin FIG. 6A. Light entering the layer 82 is refracted by one side 84 ofeach facet 85 as it enters, and then is totally internally reflected bysecond side 86 of each of the facets 85. In one form of the inventionthe redirecting layer 82 can be a “Transparent Right-Angle Film”(hereinafter, TRAF), which is a trademark of 3M Corp., and this productis commercially available from 3M Corp. This TRAF operates by refractionand total internal reflection to turn incident light throughapproximately a ninety degree angle, as would be desired in a typicalLCD backlighting application. The acceptance angle of the prior art TRAFis about twenty-one degrees, which is large enough to redirect a largefraction of light 75 which enters the low-index layer 81. In a morepreferred form of the invention, the facet angles are chosen to redirectmore of the light 75 which enters the low-index layer 81 by thedescribed mechanism of refraction plus total internal reflection. Eitherone or both of the facet surfaces 84 and 86 can be shaped to control theoutput angular distribution. For example, the use of curved facetssmoothly broadens the distribution, as well as providing a lightdiffusing effect which can improve uniformity.

[0145] In another preferred embodiment, the facet angle surfaces of theredirecting layer 82 can be varied progressively to compensate for thevariation in viewing angle with position, when viewed from typicalviewing distances. The details of such a compensation effect weredescribed earlier in reference to the design of the reflecting facetlayer in the embodiment shown in FIG. 2M. Similar principles can beapplied to the design of any faceted redirecting layer, includingrefracting layers and refracting/internally-reflecting layers. Examplesof embodiments which can, for example, make use of such progressivelyvaried faceted layers are shown in FIGS. 12E (layer 140), 12G (layer152), 12H (layer 166), 12K (layer 186), 12N (layer 210), 12O (layer228), and 12P (layer 246).

[0146] In another form of invention the layers 66 and 81 can havesimilar but slightly different indices n₂ and n_(2′), respectively. Theoperating principles of the device 10 will be substantially similar aslong as the critical angles associated with interfaces between the firstlayer 61 and the two layers 66 and 81 do not differ by more than thefirst layer convergence angle:

|arcsin (n_(2′)/n₁)−arcsin (n₂/n₁)|<φ  (7)

[0147] Therefore, in this case approximately equal fractions of thelight will enter layers 66 and 81, for further processing by theredirecting layers 70 and 82, respectively.

[0148] All forms of the invention can further include an output diffuserlayer 40, shown in phantom in FIG. 2C or transmissive or translucentdiffuser layer 83 shown in FIG. 6A. In general this diffuser layer 40can be a surface diffuser, a volume diffuser, or at least one array ofmicro lenses having at least a section of a cylinder (known as a“lenticular array”). These layers 40 and 83 can increase lightuniformity or broaden the angular distribution into ambient. Lenticulararrays are advantageous because they have low back-scattering incomparison to surface or volume diffusers, and because they have sharperoutput angle cut-offs when illuminated by collimated light. Lenticulararrays also preferentially diffuse only those features which wouldotherwise run in the general direction of the axis of each cylindricalmicro lens.

[0149] In one preferred embodiment shown in FIG. 10, the lightredirecting layer 10 makes use of flat facets 111 such that the outputlight is highly collimated. The desired output angular distribution isfurther controlled by including a lenticular diffuser 112 having anappropriate focal ratio, with its cylindrical micro lenses runningapproximately parallel to the y-axis. The lenticular diffuser 112 alsodiffuses non-uniformities which would otherwise appear to be ring in thegeneral direction of the y-axis. In this embodiment a second lenticulardiffuser 113 can be included to diffuse non-uniformities which wouldotherwise appear running in the general direction of the z-axis. Thissecond lenticular diffuser's micro lenses run approximately parallel tothe z-axis (see FIGS. 12H and 12N). Note that the order of positioningof the diffusers 112 and 113 can be interchanged without loss of opticaladvantage. Similarly, the lenticular diffuser 112 and 113 can beinverted and can have concave contours rather than convex contours shownin FIG. 10. While such changes can affect the details of theperformance, the diffuser layers 112 and 113 can still provide thegeneral advantages described.

[0150] In another preferred embodiment shown in FIG. 11, the functionsof the flat-faceted light redirecting layer 110 and the parallellenticular diffuser 112 in FIG. 10 can both be performed by a lightredirecting layer 114 having curved facets (see also, for example, FIGS.2H, 2M and 3A illustrating curved facets). These curved-facet layersredirect the light, control the angular output by having an appropriatefacet curvature, and act as a diffuser for non-uniformities running inthe general direction of the y-axis. By combining these functions in asingle-layer the number of components is reduced, which improvesthickness, cost, and manufacturability. In this embodiment, a singlelenticular diffuser 115 can be included to diffuse the remainingnon-uniformities which would otherwise appear running in the generaldirection of the z-axis. This type of lenticular diffuser micro lensruns approximately parallel to the z-axis. Note that the lenticulardiffuser 115 can be inverted and can have concave contours rather thanthe convex contours shown in FIG. 10. Again, such changes can affectperformance details, but the layers in 114 and 115 perform as intended.

[0151] In all embodiments using multiple micro-structured layers, thefacet or lenslet spacings of these layers described herein before can bechosen to have non-rational ratios, in order to avoid undesirable Moiréinteraction between layers or with a liquid crystal display.

[0152] Similar lenticular diffusers can be used with non-wedgegeometries having wedge shaped cross-actions, with similar advantages ifthe diffuser cross-sections are approximately as shown in FIGS. 10 and11. One example is the tapered disk illustrated in FIG. 5. In this casethe lenticular diffuser analogous to layer 112 in FIG. 10 would havemicro lenses whose axes run in concentric circles about the disk's axisof rotations. A diffuser analogous to the layer 113 in FIGS. 10 and 115in FIG. 11 would have micro lenses whose axes emanate radially from thedisk's central axis.

[0153] Light Sources and Couplers

[0154] In a more preferred form of the invention shown in FIGS. 2A andB, a faceted layer 30 has been included for optically redirecting thelight. The facets 34 can be integral to the layer 30 or a separate facetlayer. Details of operation of such a faceted layer have been discussedhereinbefore. As shown further in FIG. 6A an input faceted layer 74 canalso be disposed between a light source 76 and the first layer 61. Thefaceted layer 74 can be a prismatic facet array which provides acollimating effect for input light 78 which provides brighter or moreuniform output light 80 into ambient.

[0155] Linear prisms parallel to the y-axis can improve uniformity byadjusting the input angular distribution to match more closely the inputnumerical aperture. Linear prisms parallel to the x-axis can limit theoutput transverse angular distribution, and also improve outputbrightness when used with a fluorescent lamp light source. In otherforms of the invention, diffusion of input light is desirable wherein adiffuser 79 is used to diffuse the light distribution to spread out thelight to improve light uniformity. The diffuser 79 is preferably alenticular array, with cylindrical lenslets parallel to the y-axis. Thediffuser 79 can also be a standard surface or volume diffuser, and canbe a discrete film or coupled integrally to the wedge layer 61. Multipleprismatic or diffuser films can be used in combination. Such a film formof the diffuser 79 and the faceted film 74 can be interchanged inposition to vary their effects.

[0156] In another preferred form of the invention, a portion of adielectric total internally reflecting CPC portion 100 (compoundparabolic concentrator) can be interposed between the light source 76and the first layer 61 (see FIGS. 2L, 120 and 12P). The CPC portion 100adjusts the input light to match more closely the input numericalaperture. The CPC portion 100 is preferably formed integrally with thefirst layer 61.

[0157] Reflector elements 92 and 94 shown in FIGS. 7 and 8,respectively, can be shaped and positioned to maximize the throughput oflight from the light source 76 to the light-pipe aperture. This isequivalent to minimizing the reflection of light back to the lightsource 76, which partially absorbs any returned light. The light source76 is typically cylindrical and is surrounded by a transparent glassenvelope 93, each having circular cross-sections as shown in FIGS. 7 and8. Typical examples of such light sources include fluorescent tubes andlong-filament incandescent lamps. The outer diameter of the light source76 can be less than or equal to the inner diameter of the glass envelope93. FIG. 7 shows a prior art U-shaped reflector 92 formed by wrapping aspecular reflectorized polymer film around the light source 76 andmaking contact with the wedge layer 12 at each end of the film. Thereflector element 92 typically is formed into a shape which isapproximately an arc of a circle on the side of the light source 76opposite the wedge layer 12, with approximately straight sectionsconnecting each end-point of the arc with the wedge layer 12. Thismanner of coupling the reflector element 92 to the wedge layer 12 ismost easily accomplished when the reflector element cross-section lackssharp corners. In general the light source 76 is not permitted to toucheither the wedge layer 12 or the reflectorized film, in order tominimize thermal and electrical coupling which can reduce lampefficiency.

[0158] In one form of the present invention shown in FIG. 8, thereflector element 94 is advantageously designed and the light source 76is advantageously placed to minimize the fraction of light returned tothe light source 76, and thereby increases efficiency. In one preferredembodiment, at least a section of the reflector element 94 is shapedsuch that a line drawn normal to the surface of the reflector element 94at each point is tangent to the circular cross-section of the lightsource 76. The resulting reflector shape is known as an involute of thelight source 76.

[0159] While an involute provides maximum efficiency, other shapes cangenerally be more easily manufactured. Polymer films can be readily bentinto smooth curves which include almost semicircular arcs, as describedabove. It can be shown that when the cross-section of the light source76 and semicircular section of the reflector element 92 are concentricas shown in FIG. 7, then the semicircular section of the reflectorelement 92 will return all incident rays to the light source 76, leadingto poor efficiency. Such inefficiency is a general property ofself-absorbing circular sources and concentric semicircular reflectors.This general property can be derived from simple ray-tracing or theprincipal of skew invariance. Even if the reflector element 92 is notperfectly circular, each portion of the reflector element 92 will tendto return light to the light source 76 if the cross-section of the lightsource 76 is centered near the center of curvature of that reflectorsection.

[0160] In another preferred embodiment, the cross-section of thereflector element 94 in FIG. 8 includes one or more almost semicirculararcs, and efficiency is increased by displacing the center of the lightsource 76 away from the center of curvature of the reflector element 94.Ray-tracing and experiments have shown that such preferred embodimentscan be determined using the following design rules:

[0161] 1. The cross-section of the reflector element 94 has a maximumextent in the x-dimension equal to the maximum thickness of the wedgelayer 12 (or light pipe);

[0162] 2. The cross-section of the reflector element 94 has no opticallysharp corners;

[0163] 3. The radius of curvature of the reflector element 94 is aslarge as possible; and

[0164] 4. The light source 76 is as far as possible from the wedge layer12, but is far enough from the reflector element 94 to avoid contactwith worst-case manufacturing variations.

[0165]FIG. 8 shows an example of a coupler which satisfies these abovedescribed design rules for the light source 76 with inner diameter=2 mm,outer diameter=3 mm, thickness of the wedge layer 12 (or light pipe)=5mm, and manufacturing tolerances which permit a 0.25 mm spacing betweenthe reflector element 94 and the outer diameter of the glass envelope93. In this example of a preferred embodiment the radius of curvature ofthe reflector element 94 is 2.5 mm, and the center of the light source76 is displaced by 0.75 mm away from the aperture of the wedge layer 12.A coupler constructed according to this design was found to be 10-15%brighter than the comparable concentric coupler shown in FIG. 7.

[0166] The involute and the U-shaped reflector elements 92 and 94previously described are designed to output light to the aperture of thewedge layer 12 with angles approaching ±90 degrees relative to theaperture surface normal. In another preferred embodiment, the reflectorelement 94 is shaped to output light with an angular distribution whichis closer to the N.A. of the device 10. As shown in FIGS. 6B and 6C,such shapes as the reflector element 94 can include other geometries,such as, a compound parabolic source reflector 86 and a nonimagingillumination source reflector 88. An example of the source reflector 88is described in copending Ser. No. 07/732,982 assigned to the assigneeof record of the instant application, and this application isincorporated by reference herein.

[0167] In another embodiment of the invention shown in FIGS. 6D, 12L,12N, and 12O, the wedge layer 90 has a non-monotonic varying wedge crosssectional thickness over various selected portions of the wedge shapedcross section. It has been determined that one can exert control overthe light distribution being output by control of this cross section.Further, it has been determined that optical boundary effects, as wellas intrinsic light source effects, can combine to give an output lightdistribution with unwanted anomalies. One can therefore also compensatefor these anomalies, by providing a wedge cross section with nonlinearchanges in the actual dimensions of the wedge layer 90, for example,near the thicker end which typically receives the input light. Bycontrol of these dimensions one can thus have another degree of freedomto exert control over the light distribution, as well as providevirtually any design to compensate for any boundary effect or lightsource artifact. Furthermore, one can vary the index of refractionwithin the wedge layer 90 in the manner described hereinbefore to modifythe distribution of light and also compensate for light input anomaliesto provide a desired light distribution output.

[0168] Manufacture of Luminaire Devices

[0169] In one form of the invention, manufacture of the device 10 can beaccomplished by careful use of selected adhesives and laminationprocedures. For example, the wedge layer 12 having index n₁ can beadhesively bonded to the first layer 28 having index n₂. An adhesivelayer 60 (see FIG. 3B) can be applied in liquid form to the top surfaceof the first layer 28, and the layer 28 is adhesively coupled to thebottom surface 16 of the wedge layer 12. In general, the order ofcoupling the various layers can be in any given order.

[0170] In applying the layer 12 to the layer 28 and other such layers,the process of manufacture preferably accommodates the formation ofinternal layer interfaces which are substantially smooth interfacialsurfaces. If not properly prepared such internal layers candetrimentally affect performance because each interface between layersof different indices can act as a reflecting surface with its owncharacteristic critical angle. If the interfacial surfaces aresubstantially smooth, then the detrimental effect of uneven surfaces isnegligible. Therefore in effectuating the lamination of the variouslayers of the device 10, the methodology should utilize adhesives and/orjoining techniques which provide the above described smooth interfaciallayers. Examples of lamination processes include, without limitation,joining without additional adhesive layers, coatings applied to onelayer and then joined to a second layer with an adhesive and applying afilm layer with two adhesive layers (one on each layer surface to bejoined to the other).

[0171] In a preferred embodiment lamination of layers is done withoutany additional internal layer whose potential interfacial roughness willdistort the light distribution. An example of such a geometry for thedevice 10 can be a liquid layer between the wedge layer 12 and thesecond layer 30. This method works best if the first layer 29 (such asthe liquid layer) acts as an adhesive. One can choose to cure theadhesive either before, partially or completely, or after joiningtogether the various layers of the device 10. The optical interface isthus defined by the bottom surface of the wedge layer 12 and the topsurface of the second layer 30.

[0172] In another embodiment wherein a coating is used with an adhesivelayer, the first layer 28 can be the coating applied to the second layer30. Then, the coated film can be laminated to the wedge layer 12 in asecond step by applying an adhesive between the coated film and thewedge layer 12. It is preferable to apply the low index coating to thesecond layer 30 rather than directly to the wedge layer 12 since thesecond layer 30 is typically supplied in the form of continuous filmrolls. In practice it is more cost effective to coat such continuousrolls than to coat discrete pieces. With this methodology it is moreconvenient to control thickness of the applied low index layer.

[0173] In another embodiment, the second layer 30 is manufactured insuch a way that it adheres to the first layer 28 directly without use ofadditional adhesives. For example, the second layer 30 can bemanufactured by applying a layer of polymer material to the first layer28, and then casting this material to have the desired second layergeometry. In another example, the first layer 28 can serve as a carrierfilm during the embossing of the second layer 30. By use of appropriatetemperatures during the embossing process, the second layer 30 can beheat-fused to the first layer 28. Such heat-fusing can be accomplishedusing a conventional FEP first-layer film by embossing at almost fivehundred degrees F. or higher.

[0174] In a further embodiment using a film and two adhesives, the firstlayer 28 can be an extruded or cast film which is then laminated to thewedge layer 12, or between the wedge layer 12 and the second layer 30using adhesive between the two types of interfaces. In order to minimizethe detrimental light scattering described hereinbefore, the adhesivelayer should be flat and smooth. The film can be obtained as a low indexmaterial in commercially available, inexpensive forms. Such additionaladhesive layers can increase the strength by virtue of the multi-layerconstruction having adhesive between each of the layers.

[0175] In the use of adhesive generally, the performance of the device10 is optimized when the index of the adhesive between the wedge layerand the first layer is as close as possible to the index of the firstlayer 28. When the critical angle at the wedge/adhesive interface is aslow as possible, then the light undergoes a minimal number ofreflections off the lower quality film interface before exiting thedevice 10. In addition, the index change at the surface of the firstlayer film is minimized which decreases the effects of film surfaceroughness.

[0176] Manufacture of faceted surfaces can be accomplished bymicro-machining a mold using a master tool. Machining can be carried outby ruling with an appropriately shaped diamond tool. The master tool canbe replicated by known techniques, such as electroforming or casting.Each replication step inverts the shape of the desired surface. Theresulting mold or replicates thereof can then be used to emboss thedesired shape in the second layer 30. A directly ruled surface can alsobe used, but the above described embossing method is preferred. Known“milling” processes can include chemical etching techniques, ion beametching and laser beam milling.

[0177] In yet another method of mechanical manufacture, the facetedsurface 34 (see FIGS. 2B and 2M, for example) is manufactured by awelding process, such as embossing or casting, using a hard tool whichhas on one surface the inverse of the profile of the desired facetedsurface 34. Therefore, the manufacturing problem reduces to the matterof machining an appropriate tool. Usually the machined tool is used as atemplate to form the tools actually used in the casting or embossingprocess. Tools are typically replicated by electroforming. Sinceelectroforming inverts the surface profile, and electroforms may be madefrom other electroforms, any number of such inversions can beaccomplished and the directly machined “master” can have the shape ofthe faceted surfaces 3A or its inverse.

[0178] The tooling for the faceted surface 34 can be manufactured bysingle-point diamond machining, wherein the distance between cuttingtool and the work is varied to trace out the desired profile. Thediamond cutting tool must be very sharp, but in principle nearlyarbitrary profiles can be created. A given design can also requirespecific adaptations to accommodate the non-zero radius of the cuttingtool. If curved facet surfaces are required, then circular arcs arepreferred to facilitate fabrication. The cutting tool is moved throughthe cutting substrate and cuts a groove having the approximate shape ofthe tool. It is desirable to machine the entire piece using a singlediamond tool. When this method is used for making a “focusing” type ofthe faceted surface 34, the variable groove profile therefore should bedesigned such that the various groove profiles can be machined by thesame tool. The required shape variations can still be accomplished byvarying the angle of the tool, as well as the groove spacing and depth.

[0179] Design of the faceted surface 34 preferably satisfies a fewgeneral constraints:

[0180] 1. Approximately linear variation in the center of theillumination angular distribution as a function of position. A variationof 11 degrees (±5.5°) from top to bottom of typical computer screens iseffective;

[0181] 2. The width of the variable angular distribution of light outputshould be approximately proportional to the local illuminance in orderto achieve approximately uniform brightness to an observer. Examplesgiven below show the spatial distribution is approximately uniform, sothe angular cones have approximately uniform width; and

[0182] 3. Spacing between grooves of the facets 38 should be largeenough or irregular enough to avoid diffraction effects, but also bechosen to avoid Moiré patterns when used with an LCD panel. In practicethese requirements limit the allowed spatial variations.

[0183] In the manufacture of the device 10, for example, the viewingangle depends on the tilt and curvature of each of the facets 38.Focusing is accomplished by rotating the facet structure as a functionof position. Using the example of a 150 mm screen viewed from 500 mmaway, the illumination cone can be varied by 17 degrees (i.e., ±8.5degrees) from top to bottom. For typical materials, acrylic and FEP,this requires the facet structure to rotate by approximately 5.7 degreesfrom top to bottom of the screen 89 (see FIG. 9B).

[0184] Design constraints can result when limitations (1)-(3) arecombined with the need to machine variable curved grooves with a singletool. For example, maintaining a constant angular width (Constraint #1)at a constant cutting depth requires a compensating variation in groovespacing or groove depth. Specifically, a linear change in groove spacingcan reduce the brightness variation to a negligible level when the formtool which cuts the groove is shaped so that portions of each curvedreflector facets (see FIG. 2M) are shadowed by the top edge of theadjacent facets. This spacing variation can be small enough to satisfyConstraint #3.

[0185] Further methods of manufacture can include vapor deposition,sputtering or ion beam deposition of the first layer 28 since this layercan be quite thin as described hereinbefore. Likewise, the second layer30 can be controllably applied to form the faceted layer 30 shown inFIG. 2B (such as by masking and layer deposition).

[0186] Wedge Light Pipe as a Simple Collimator Device

[0187] In the most general embodiment the wedge layer 12 can function inthe context of the combination as a simple collimating optical element.The substantially transparent wedge layer 12 has an optical index ofrefraction n₁ and the top surface 14 and the bottom surface 16 convergeto establish at least one angle of inclination φ (see FIG. 15). Thewedge layer 12 also includes the back surface 20 spanning the topsurface 14 and the bottom surface 16. Adjacent to the wedge layer 12 isthe transparent first layer 28 having index of refraction n₂ includingan air gap. Adjacent to the first layer 28 is a specular reflectivelayer, such as the faceted surface 34 of the second layer 30.

[0188] Substantially uncollimated light is introduced through the backsurface 20 by the source 22. The light propagates within the wedge layer12, with each ray decreasing its incident angle with respect to the topand bottom surfaces 14 and 16 until the incident angle is less than thecritical angle θ_(c). Once the angle is less than θ_(c), the ray emergesinto ambient. Rays which emerge through the bottom surface 16 arereflected back into the wedge layer 12 and then output into ambient. Byvirtue of the angle-filtering effect previously described, the outputlight is collimated within a cone of angular width approximately:

Δθ≅2 φ^(1/2)(n ²−1)^(1/4)  (8)

[0189] An area 99 to be illuminated lies beyond the end of the wedgelayer 12 and substantially within the above-defined cone of width Δθ.

[0190] In another preferred embodiment a light-redirecting means can bepositioned beyond the end of the wedge layer 12 and substantially withinthe above-defined cone of width Δθ. The light-redirecting means can be alens, planar specular reflector, or curved reflector. Thelight-redirecting means reflects or refracts the light to the area to beilluminated. Further details and uses of such redirecting means, such aslenticular diffusers, will be described hereinafter.

[0191] In the embodiments of FIG. 6 having two air gaps or transparentdielectric layers, the light redirecting layers are independent, andthus one can construct devices having layers of different types. Forexample, the use of two transmissive redirecting layers is preferredwhen light is to be emitted from both sides of the device 10 or whenevermaximum collimation is desired. Examples of the redirecting layer 82 ingeneral for all inventions for two redirecting layers can include theexamples in FIG. 12 where the letter in parenthesis corresponds to theappropriate figure of FIG. 12: (a) diffraction gratings 120 or ahologram 122 in FIG. 12A, (b) two refracting facet layers 124 withdiffusers 126 in FIG. 12B, (c) two faceted layers 128 with facets 130designed to refract and internally reflect light output from the wedgelayer 12; such facets 130 are capable of turning the light outputthrough a larger angle than is possible by refraction alone; (d) tworefracting single facet layers 132 (prisms); (e) a top surfaceredirecting layer for the wedge layer 12 having a refracting singlefacet layer 134 with a curved output surface 136 for focusing. A bottomsurface. 138 includes a redirecting layer for refracting and internallyreflecting light using a faceted layer 140; facet angles are varied withposition to focus output light 142 at F; (f) a top surface redirectinglayer 144 comprised of a refracting faceted layer 146 and a bottomredirecting layer comprised of a refracting/internally reflecting layer148 with narrow angle output for the light, and a diffuser layer 150 canbe added to smoothly broaden the light output angular distribution; (g)a top surface redirecting layer of refracting/internally reflectingfaceted layer 152 with refracting surfaces 154 convexly curved tobroaden the output angular distribution; the facet angles can be variedwith position and thereby selectively direct the light output angularcones to create a preferred viewing region at a finite distance; thisarrangement can further include a transverse lenticular diffuser 156 todiffuse nonuniformities not removed by the curved facet layer 152; thebottom redirecting layer comprises a refracting/internally reflectingfaceted layer 158 with a reflecting surface 160 being concavely curvedto broaden the light output angular distribution in a controlled manner;(h) a top redirecting layer, including a refracting faceted layer 162with curved facets 164 to broaden the output angular distribution in acontrolled manner and to improve uniformity; a bottom redirecting layer,including a refracting/internally-reflecting faceted layer 166 with flatfacets 168 for narrow-angle output with facet geometry varied withposition to focus output light at a finite distance; a parallellenticular diffuser 170 can be used to smoothly broaden the outputangular distribution in a controlled manner and to improve uniformity;the transparent image shown in phantom can be printed on or adhesivelybased to a lenticular diffuser; a transverse lenticular diffuser 172 isused to diffuse non-uniformities not removed by the parallel lenticulardiffuser 170. The combination of a focused flat-faceted layer 166 andthe diffuser 170 cooperate to create a preferred viewing zone at afinite distance, similar to using focused curved facets. Also shown isan LCD component 173 (in phantom) usable with this and any other form ofthe device 10 for illumination purposes.

[0192] In other architectures, one transmissive and one reflectiveredirecting layer can be combined. These are combinations of reflectiveredirecting layers with the various types of transmissive redirectinglayers discussed above. Reflective redirecting layers can be specular,partially diffuse, diffuse, faceted or any combination thereof. Thesearchitectures are preferred when light emission is desired from one sideonly, or in some cases when minimum cost is paramount. Examples of sucharchitectures are in FIG. 12: (i) a bottom surface specular reflector174 combined with a top layer transmission diffraction grating ortransmission hologram 176; (j) a bottom surface specular reflector 178combined with a top surface refracting faceted layer 180, with adiffuser 182 (shown in phantom in FIG. 12J and an interveningimage-forming layer 171; (k) a bottom layer specular reflector 184 witha top layer refracting/internally-reflecting faceted layer 186, withfacet geometry being varied with position to focus output light at afinite distance; a diffuser 188 is shown in phantom; (l) a bottom layerspecular reflector 190 with a top layer refracting/internally-reflectingfaceted layer 192, and curved facets 194 are used to smoothly broadenthe angular output of light in a controlled manner and to improveuniformity. The thickness of the wedge layer 12 and of both top andbottom surface low-index layers 196 (e.g., air gaps) are varied toinfluence the light output spatial distribution; (m) a bottom reflector198 is partially specular, partially diffuse to improve uniformity; FIG.12M shows the initial reflector section made controllably diffuse byaddition of an integral lenticular diffuser 200; the diffuser 200 isdesigned to selectively reduce nonuniformities which would otherwiseappear in the output near the thicker end, and running in the generaldirection of the y-axis; also included is a top redirecting layer 202which is refracting/internally-reflecting and has a reflecting surfacewhich is curved; and (n) a bottom reflector layer 204 which is partiallyspecular, partially diffuse to improve uniformity; FIG. 12N shows: theinitial reflector section 206 which is slightly roughened to reducespecularity, and thereby selectively reduces nonuniformities which wouldotherwise appear in the output near thicker end 208; a top redirectinglayer 210 is used which is refracting/internally-reflecting with aflat-faceted layer 212, and the facet geometry is varied to redirectlight from each facet to a common focus at finite distance; a transverselenticular diffuser 213 is shown in phantom; a parallel lenticulardiffuser 214 is used to smoothly broaden the output angular distributionin a controlled manner, converting the focal zone of the flat-facetedlayer 212 to a wider preferred viewing zone; the lenticular diffuser 213also improves uniformity; an LCD display 216 or other transparent imageis show in phantom; (o) in a preferred embodiment an eccentric coupler218 uses a uniformity-enhancing lenticular diffuser 220 shown in phantomin FIG. 120. A converging tapered section 222 or CPC (integral to thewedge layer) transforms the output angular distribution to match moreclosely the input N.A. of the wedge layer 12. The wedge layer 12thickness is smoothly varied to influence output spatial distributionand improve uniformity; a bottom redirecting layer 224 is a specular orpartially diffuse reflector; a top redirecting layer 226 is arefracting/internally-reflecting faceted layer 228 with reflectingsurfaces 230 convexly curved to smoothly broaden output angle in acontrollable manner; facet geometry is varied with position toselectively direct the angular cone of light from each face to create apreferred viewing zone 232 at a finite distance; a transverse lenticulardiffuser 234 is shown in phantom; an LCD display 236 or othertransparent image is also shown in phantom; the more convergingN.A.-matching section is advantageous in combination with the facetedredirecting layers, because the redirecting and low-index layers do notneed to overly the more converging section; therefore, the inputaperture (and thus efficiency) of the device 10 is increased withminimum increase in total thickness of the device; (p) another preferredembodiment for LCD backlighting uses an eccentric coupler with auniformity-enhancing diffuser shown in phantom in FIG. 12P; a converginghalf-tapered section 240 or half-CPC (integral to the wedge layer 12)transforms a coupler output angular distribution to match more closelythe input N.A. of the wedge layer 12. A diffser 239 (in phantom) canalso be interposed between light source 217 and the wedge layer 12. Thesufficiently truncated half-CPC 240 is just a simple tapered section. Abottom reflector 242 which is partially specular, partially diffuse isused to improve uniformity; FIG. 12P further shows an initial reflectorsection 244 which is slightly roughened to reduce specularity, oralternatively shaped into a series of parallel reflective grooves, whichthereby selectively reduces nonuniformities which would otherwise appearin the output near the thicker end; a top redirecting layer 246 is arefracting/internally-reflecting faceted layer 248, with refractingsurfaces 250 convexly curved to smoothly broaden output angle in acontrollable manner; facet geometry is varied with position toselectively direct angular cones of light from each facet to create apreferred viewing zone at a finite distance; a transverse lenticulardiffuser 252 is shown in phantom Also included is an LCD display 254 orother transparent image shown in phantom.

[0193] The more converging N.A.-matching section (such as half taperedsection 240) is advantageous in combination with the faceted redirectinglayers, because the redirecting and low-index layers do not need tooverly the more converging section; therefore, the light-acceptingaperture of the device 10 is increased without increasing the totalthickness. The advantage is also conferred by the fully-tapered section222 shown in FIG. 120; but in comparison the half-tapered section 240 inFIG. 12P provides greater thickness reduction on one side, at theexpense of being longer in the direction of taper for equivalentN.A.-matching effect. It can be desirable to concentrate the thicknessreduction to one side as shown, because the top surface low-index layercan be made thicker to improve uniformity. This configuration can bemore easily manufactured because the bottom reflector layer can beintegral to the coupler reflector cavity, without need to bend areflective film around a corner; (q) a bottom specular or diffuselyreflecting layer 256 can be combined with single-facet refracting toplayer 258 in yet another embodiment (see FIG. 12Q); and (r) in cases forinterior lighting usage, a bimodal “bat-wing” angular light distribution260 is preferred; in FIG. 12R is shown a top refracting layer 262 withfacets 264 and has a curved front surface 266 to smoothly broadenangular output and improve uniformity, with output light directedprimarily into a forward quadrant; a bottom reflecting layer 268reflects light primarily through a back surface of a top redirectinglayer, with output directed substantially into a backwards quadrant.

[0194] As understood in the art the various elements shown in thefigures can be utilized with combinations of elements in taperedluminaire devices. Examples of two such combination geometries are shownin FIGS. 13 and 14, each figure also including features specific to thegeometry shown. As illustrated in FIG. 13, two wedges 276 can becombined and formed integrally. This combination can provide higherbrightness than a single wedge having the same extent because it permitstwo light sources to supply light to the same total area. Whilebrightness is increased for this device, efficiency is similar becausetwo sources also require twice as much power as one source. Aredirecting film 272 with facets 274 can be a single, symmetric designwhich accepts light from both directions as shown. Alternatively, theredirecting film 272 can have a different design for each wing of thebutterfly.

[0195] In FIG. 14 is shown a three dimensional rendition of a tapereddisk 270, such as shown in FIG. 5, and is sectioned to show theappearance of the various layers. A faceted redirecting layer 280comprises concentric circular facets 282 overlying a tapered light-pipeportion 284. Directly over a light source 288, overlying the gap at theaxis of the light-pipe portion 284, the redirecting layer 280 takes theform of a lens (a Fresnel lens 280 is shown, for example). Directlybelow the light source 288 is a reflector 290 positioned to preventlight from escaping and to redirect the light into the light-pipeportion 284 or through the lens. At least one opening is provided in thereflector to permit passage of elements, such as wires or light-pipes.

[0196] Use of Imaging or Colored Layers

[0197] All embodiments of the invention can incorporate one or morelayers which have variable transmission to form an image, or whichimpart color to at least a portion of the angular output. Theimage-forming layer can include a static image, such as a conventionaltransparent display, or a selectively controlled image, such as a liquidcrystal display. The image-forming or color-imparting layer can overlayone of the redirecting layers, or alternatively it can comprise anintermediate layer between one of the low-index layers and theassociated redirecting layer, or an internal component of a redirectinglayer. For example, overlying image-forming layers 129 are shown inphantom in FIGS. 12C and 12G. Examples of an internal image-forminglayer 171 are shown in FIGS. 12H and 12J.

[0198] In one preferred embodiment, the image-forming layer (such as 129and 170) is a polymer-dispersed liquid crystal (PDLC) layer. By properarrangement of the layers, the image or color may be projected from thedevice within selected portions of the output angular distribution. Theimage or selected color can be substantially absent in the remainingportions of the output angular distribution.

[0199] Bi-modal Reflective Wedge for LCD Panel Illumination

[0200] In some applications it is desired to illuminate a single LCDpanel selectively with either ambient light or by active back-lighting.In these applications ambient illumination is selected in well-litenvironments in order to minimize power consumption by the display. Whenavailable environmental illumination is too low to provide adequatedisplay quality, then active backlighting is selected. This selectivebi-modal operating mode requires a back-illumination unit which canefficiently backlight the LCD in active mode, and efficiently reflectambient light in the alternative ambient mode.

[0201] The most widespread prior art bi-modal liquid crystal display isthe “transflective display” 101, such as is shown in FIG. 16B. Thisapproach uses a conventional backlight 102 and a transmissive LCD panel103, with an intervening layer 104 which is partially reflective andpartially transmissive. In order to achieve adequate ambient modeperformance, it is typically necessary for the intervening layer 104 tobe 80-90% reflective. The resulting low transmissivity makes thetransflective display 101 inefficient in the active mode of operation.

[0202] Another embodiment of the invention is shown in FIG. 17. Thisembodiment outperforms prior art transflective displays in the activemode, and demonstrates comparable performance in the ambient mode. Inthis embodiment the wedge layer 12 (index=n₁) having the bottom surface16 is coupled to a transparent layer 28 of index n₂<n₁, which can be anair gap. The n₂ layer is coupled to a partially diffuse reflector layer105. This reflector layer 105 is, for example, preferably similar to thereflectors used in conventional LCD panels used in ambient mode only, asshown in FIG. 16A. Overlaying the wedge layer top surface 14 is afaceted redirecting layer 106, such as a lenticular diffuser with microlenses approximately parallel to the y-axis. A liquid crystal displaypanel 107 overlays the faceted redirecting layer 106. The back surface20 of the wedge layer 12 is coupled to the light source 22.

[0203] The lenticular redirecting layer 106 and the wedge-layer 12 aresubstantially transparent to the incident and reflective light, so thatin ambient mode the device 10 operates in a manner similar toconventional ambient-mode-only displays. When an active mode isselected, the light source 22 is activated, and the multiple layers actto spread the light substantially uniformly over the device 10 by virtueof the relationship between the indices of refraction and convergenceangles of the layers, as described before. The resulting uniformillumination is emitted through the top surface 14 of the wedge layer12. In a preferred embodiment, the reflector layer 105 is nearlyspecular in order to maximize ambient-mode performance. In thispreferred embodiment the light emitted from the top surface is emittedlargely at grazing angles, unsuitable for transmission by the LCDdisplay panel 107. The redirecting layer 106 redirects a fraction ofthis light by a combination of refraction and total internal reflection,as described hereinbefore. The redirecting layer 106 is preferablydesigned such that at least 10-20% of the light is redirected intoangles less than 30 degrees from the LCD normal, because typically theLCD transmission is highest in this angular range. It is sufficient todirect only a fraction of the back-illumination into suitable angles,because the prior art transflective display is quite inefficient in theactive mode of operation.

[0204] Processing Polarized Light

[0205] In another aspect of the invention, the light being processed bythe optical device 10 has an inherent polarization (such as, linear,circular and elliptical) that can be used to advantage in improving theillumination from a liquid crystal display (“LCD”) system or otheroutput which depends on using polarized light. In a system which employsan LCD, it is necessary to remove one type of polarized light 308 andpass to the LCD layer only the other type of polarized light. Forexample in FIG. 30 a conventional polarization layer 312 preferentiallyabsorbs one polarization of light amounting to about one-half the inputlight from light source 306, with the preferred polarization light beingtransmitted to LCD layer 316. The polarized light of the properpolarization is processed by the liquid crystals and a second polarizer314 in the desired manner to provide the displayed feature of interest.In such a conventional system about half the light from the light sourceis “unwanted” and thus is lost for purposes of providing an LCD outputof interest. Consequently, if a means could be found to utilize bothtypes of polarized light (not removing light of an unwantedpolarization), a substantial gain in efficiency and brightness canresult for the liquid crystal display. The subject invention is directedin part to that end, and the following embodiments are preferredstructures and methods for accomplishing that goal.

[0206] In the most general explanation of a polarization filter,referring to FIG. 30B, the function of a polarization filter layer 307is to take the input light 308 consisting of two polarization states oftype 1 and 2 and create transmitted light 309 consisting of polarizationstates 3 and 4 and reflected light 311 consisting of polarization states5 and 6. This can be related to our specific references hereinafter to a“first” and “second” state as “states” 1,3 and 5 as the “firstpolarization light 218” and 2,4 and 6 as the “second polarization” light220. Thus, we assume that the form of states 3 and 5 are chosen so thatthey alone specify the light that is transmitted and reflected due tothe light portion incident in polarization state 1, and let states 4 and6 be associated with polarization state 2. However, the form of thepolarization states need not be related in any more specific way. Forsome range of incident angles over some spectral wavelength range andfor some specific selection of input polarization states, thepolarization filter layer 307 processes the input light 308 and producesoutput light 309 with a specific total power relationship. If we definethe powers (P_(i)) in each of the polarization states (i, wherei=1,2,3,4,5,6), the condition is:$\frac{P_{3`}}{P_{1}} > \frac{P_{4}}{P_{2}}$

[0207] By definition, any layer which exhibits the above characteristicsover a suitable angular and spectral range is a form of the polarizationfilter layer 307. Generally, the polarization states considered can beof arbitrary type such as linear, circular, or elliptical. In latersections we will quantify the performance of the polarization filterlayer 307 by a degree of polarization (P_(T)) defined as:${P_{T} = {{\frac{T_{31} - T_{42}}{T_{31} + T_{42}}\quad {where}\quad T_{31}} = \frac{P_{3}}{P_{1}}}},{T_{42} = \frac{P_{4}}{P_{2}}}$

[0208] For lossless layers, the transmittance is related to thereflectance, R, by

T ₃₁=1−R ₅₁ ,T ₄₂=1−R ₆₂

[0209] where

R ₅ =P ₅ /P ₁ and R ₆₂ =P ₆ /P ₂

[0210] There are a variety of implementations of a layer medium whichhas the properties described above for the polarization filter layer307. These include, but are not restricted to, implementationscontaining one or more of the following types of layers: (1) thin-filmlayers produced by coating, extrusion, or some other process which areeither non-birefringent or birefringent and are designed to operate asoptical interference coatings; (2) “thick” film layers which are morethan a single quarter wavelength optically thick somewhere in thespectral band of interest and may be produced by stacking, coating,extrusion, lamination, or some other process and are designed to operateas a Brewster Stack even when the angles and indexes do not exactlymatch the Brewster angle conditions; (3) a combination of the thin-filmand thick film approaches; (4) correlated, partially correlated, oruncorrelated surface roughness or profile which results in polarizationdependent scattering and produced by any method including etching,embossing, micro-machining, or other method; (5) and layers based ondichroic material. In general, an aggregate layer formed by one or morethe above layer types is a suitable form of the polarization filterlayer 307 layer if it satisfies the general functional specificationsdescribed above for polarization filter layers.

[0211] The implementations of the polarization filter layer 307 canconsist of either tin-film or thick-film birefringent ornon-birefringent layers. Particular examples and discussion ofbirefringent layers will be provided in a labeled subsection presentedhereinafter.

[0212] One example embodiment of a thick film form of the polarizationfilter layer 307 is based on a specific design center wavelength (6_(o))and a specific design operating angle (³inc) as shown in FIG. 30C andbased on isotropic planar layers. Layers 313 in this design exampleconsist of two types of alternating layers, called high (H) layer 314and low (L) layer 315 of optical refractive index n_(H) and n_(L)respectively. From Snell's law, we know the angle with respect to thesurface normals (3_(L), 3_(H)) at which the light 317 are traveling inany of the layer 313 in terms of the refractive indexes of the layers(n_(inc), n_(L), n_(H)) if we know the incidence angle. This implies:

n_(inc) sin θ_(inc)=n_(L) sin θ_(L)

n_(inc) sin θ_(inc)=n_(H) sin θ_(H)

[0213] For p-polarized form of the light 317 incident on an interfacebetween two optically isotropic regions, there is an angle called theBrewster's Angle at which the reflectivity of the interface is zero.This angle measured to the surface normal (θ_(H/L), θ_(L/H)) is:$\begin{matrix}{{\tan \quad \theta_{H/L}} = \frac{n_{L}}{n_{H}}} \\{{\tan \quad \theta_{L/H}} = \frac{n_{H}}{n_{L}}}\end{matrix}$

[0214] The reflectivity of the interfaces to s-polarized light atBrewster's Angle can be significant. The layers 313 which preferentiallytransmits the p-polarization state is designed by spacing theseinterfaces by quarter-wave optical thicknesses. Such quarter wavelengththicknesses (t_(L), t_(H)) are given by: $\begin{matrix}{t_{L} = \frac{\lambda_{o}}{4n_{L}\cos \quad \theta_{L}}} \\{t_{H} = \frac{\lambda_{o}}{4n_{H}\cos \quad \theta_{H}}}\end{matrix}$

[0215] One can show that the H and L indexes of refraction are relatedby the design equation:$\left( \frac{n_{L}}{n_{H}} \right)^{2} = \frac{\left( \frac{n_{inc}}{n_{H}} \right)^{2}\sin^{2}\theta_{inc}}{1 - {\left( \frac{n_{inc}}{n_{H}} \right)^{2}\sin^{2}\theta_{inc}}}$

[0216] As an example consider the specific case of:

n_(H)=1.5,n_(inc)=1.0, θ_(inc)=80°, λ_(o)=500 nm

[0217] This implies that the design index of refraction of the low indexlayer and the physical thicknesses of the low and high index layers 314and 315 should be respectively n_(L)=1.31,t_(L)=145 nm, t_(H)=110 nm.These can be achieved by using sputtered glass and vacuum depositedlithium chloride for n_(H)=1.5 and n_(L)1.31, respectively. Assumingthat the design is a matched design as in FIG. 30C, with the layers 313surrounded by an index of refraction of 1.5, the reflectivity can beeasily calculated with the well-known Rouard's Method. This matchingassumption is quite general as the outer surfaces could always beanti-reflection coated. The reflectivity for a variety of basic layercounts for the layers 313 is shown in Table 1 below: TABLE 1 Performancedata for the polarization filter layer 307 Layer Count s-ReflectivityP_(T) 1 0.069 0.036 5 0.45 0.29 11 0.85 0.75 15 0.95 0.90 21 0.99 0.98

[0218] There are a variety of similar alternative designs. More than asingle refractive index may be used as part of the thin-film structureof the layers 313. The surrounding layers need not be air and the exactnumber of low and high index layers is variable. The carrier orsubstrate could have other refractive index values. The layers 313 canbe varied from their quarter-wave thickness at the design angle and thewavelength so as to improve spectral and angular bandwidths. In fact,the operability of the layers 313 can be quite broad band and theBrewster angle design does not have to be followed with great precisionin index and angle. For example, you can trade off s-reflectivity withp-transmission by changing refractive indexes. The whole system can beflipped without changing its function.

[0219] A variety of preferred embodiments include at least two layers ofdifferent indices. Such arrangements have the n_(H) and n_(L) such thatn_(H)/n_(L)>1.15 in order to minimize the number of layers required forhigh polarization selectivity. Further, optical interference is mostpreferably used to enhance performance by using at least one layer withindex n and thickness t such that 50 nm/(n²−1)^(1/2)<t<350nm/(n²−1)^(1/2). This relationship derives from the equations providedhereinbefore regarding t_(L) and t_(H), by noting that the wavelength isin the visible light range 400 nm to 700 nm, that the incident light isnear the critical angle so that n sin θ1 and optical interferenceeffects are promoted by layers with an optical thickness between ⅛ and ½of the light wavelength. Materials and methods for fabricating suchlayers are well-known in the art of multi-layer dielectric coatings.

[0220] The Brewster Stack approach is similar to the tin-film approachdescribed above except that the layers are many wavelengths thick andtend to function largely on the basis of the incoherent addition of thewaves rather than the coherent effect that occurs in opticalinterference coatings. The design of this form of the polarizationfilter layer 307 is the same as the design of the thin-film polarizeddescribed above except that layer thicknesses are not important as longas they are at least several wavelengths thick optically. The lack ofoptical thickness effects suggests that the performance of the BrewsterStack implementation should generally be less sensitive to spectralwavelength and angular variations. The transmission ratio defined interms of the transmission of the s and p polarized light (T_(s),T_(p))of the set of N layer pairs in the geometry of FIG. 30D can be estimatedusing the approximate formula:${T_{s}/T_{p}} \approx \left\lbrack \frac{4\left( {n_{H}^{2} - 1} \right)}{n_{H}^{4}} \right\rbrack^{2N}$

[0221] The results of applying this formula to a geometry with varyingnumbers of layer pairs is shown in Table 2 below: TABLE 2 Performancedata for a Brewster Stack Form of the Filter Layer 307 Layer PairsT_(s)/T_(p) P_(T) 1 0.9755 — 20 0.61 — 50 0.29 0.55 100 0.08 0.85

[0222] Generally speaking, this type of the polarization filter layer307 requires much larger index differences and many more layers for thesame reflectivities. There is no sharp dividing line between thethin-film design and the Brewster stack approach. As thicknessincreases, coherence effects slowly decrease and beyond some point whichis dependent on the spectral bandwidth of the light signal, thecoherence effects become small compared to incoherent effects. Theseexamples described herein are simply the extreme of cases of thecoherent and incoherent situations.

[0223] In FIG. 19 are shown variations on one form of a polarized lightluminaire system 204. In particular, in FIG. 19B, the system 204includes a base layer 206 having a wedge-shaped, cross-sectional areawith optical index of refraction n₁, and a first surface 208 and secondsurface 210 converging to define at least one angle of inclination Φ.The base layer 206 further includes a back surface 211 spanning thefirst surface 208 and the second surface 210. Light 212 injected by asource (not shown) through the back surface 211 reflects from the firstand second surfaces and exits the base layer 206 when the light 212decreases its angle of incidence relative to a normal to the first andsecond surfaces with each reflection from the surfaces 208 and 210 untilthe angle is less than a critical angle 3_(c) characteristic of aninterface between the base layer 206 and a first layer means, such as alayer 214. This layer 214 includes at least a layer portion having indexn₂ less than n₁ disposed beyond the second surface 210 relative to thebase layer 206. The first layer 214 enables the light 212 to enter thefirst layer 214 after output from the base layer 206 when the light 212in the base layer 206 achieves the angle of incidence less than thecritical angle 3_(c) characteristic of an interface between the baselayer 206 and the layer portion having index n₂ in the layer 214.

[0224] The system 204 also includes a layer means for preferentialprocessing of polarized light of one state relative to another state,such as a polarization filter layer 216 (see previous genericdescription of the polarization filter layer 307). In addition to thesamples described for the filter layer 307, a further example of thepolarization filter layer 216 is a birefringent material which will bedescribed hereinafter in the context of particular embodiments in aseparate subsection. In FIG. 19, the injected light 212 includes light218 of a first polarization and light 220 of a second polarization. Thefilter layer 216 then interacts with the light 212 to preferably outputthe light 218 of a first polarization state compared to the light 220 ofa second polarization state. This filter layer 216 is disposed beyondthe second surface 210 relative to the base layer 206, and this filterlayer 216 is also able to reflect at least part of the light 220. Thisreflected light 220 is then transmitted through both the first layer 214and the base layer 206 and into a medium 207 having index n₃ (such asair). The light 218 on the other hand is output from the system 204 onthe side of the base layer 206 having the polarization filter layer 216.In FIG. 19B, the light 218 is shown being output into a media 221 havingindex n4. In this embodiment in FIG. 19B, the relationship among indicesis:

n ₄ ≧n ₂ and

arcsin (n ₂ /n ₁)−2Φ<arcsin (n ₂ /n ₁)<arcsin (n ₂ /n ₁)+2Φ  (9)

[0225] In this preferred embodiment n₂ and n₃ can be air layers with “n”being approximately one.

[0226] This same index relationship can apply to FIG. 19A which is avariation on FIG. 19B, but the first layer 214 of index n₂ is disposedfurther from the base layer 206 than the polarization filter layer 216.In the embodiment of FIG. 19B, the first layer 214 is closer to the baselayer 206 than the polarization filter layer 216.

[0227] In another embodiment shown in FIG. 19C, the indices are suchthat Equation (10) below is followed and this results in the light 220of second polarization state continuing to undergo internal reflection,rather than exiting through the first surface 208 as shown in FIGS. 19Aand 19B. The angle of incidence made relative to the polarization filterlayer 216 decreases with each cyclic reflection. The index n₃ can thusbe made small enough such that the light 220 will decrease its anglebeyond the range where the filter layer 216 exhibits its preferredreflectivity of the light 220. Consequently, at least part of the light220 can pass through the second surface 210, but is separated in angleof output relative to the light 218 of first polarization state. In theembodiment of FIG. 19C the indices have the following relationship:

[0228]n ₄ ≧n ₂ and arcsin (n ₁ /n ₁)<arcsin (n ₂ /n ₁)−4Φ  (10)

[0229] The polarization filter layer 216 most preferably outputs thelight 218 and reflects the light 220 when the angle of incidence isgreater than:

θ_(p)=arcsin [1-4Φ((n ₁ /n ₂)²−1)^(1/2)]  (11)

[0230] When light is incident at angles less than 3p, the filter layer216 can therefore be substantially transparent to light of bothpolarization states (i.e., the light 218 and the light 220).

[0231] In another embodiment of the invention shown in, for example,FIGS. 20A-C, the system 204 includes light redirecting means, such as alight reflector layer 222 in FIG. 20A, or more generically, a lightredirecting layer 224 as shown in FIGS. 20B and 20C. In general for theinventions of the device 10 (system 204 in FIG. 20), we can define lightredirecting means in terms of the propagation directions of light raysincident on, and departing from the light redirecting layer 224.Consider the case of a light ray propagating parallel to a unit vector{overscore (r)}_(i) in an optical medium having an index of refractionn_(i). If {overscore (u)}is a unit vector perpendicular to theredirecting layer 224 at the point of light ray incidence and directedaway from the redirecting layer 224 toward the side from which theincident light ray originates, then the incident light ray interactswith the light redirecting layer 224 to produce light rays which departfrom the region of interaction. If the departing light rays propagateparallel to a distribution of unit vectors {overscore (r)}_(c) in anoptical medium having index of refraction n_(c), then light redirectingmeans includes any layer which processes the incident light ray suchthat the departing light ray has one of the following properties withrespect to incident light rays throughout the operative angular range:

(1) n_(c)({overscore (r)}_(c)×{overscore (u)}) is not equal ton_(i)({overscore (r)}_(i)×{overscore (u)}) for at least 250/of thedeparting light rays;  (12)

(2) {overscore (r)} _(c) ={overscore (r)} _(i)−2({overscore(u)}·{overscore (r)} _(i)){overscore (u)} for at least 90% of thedeparting light rays.  (13)

[0232] The light redirecting layer 224 can redirect light according tocondition (1) in Equation (12) if (a) the light interacts with opticalsurfaces which are rough, (b) if the light interacts with opticalsurfaces which have a different slope from the incident surface, or (c)if the redirecting layer 224 diffracts the light into appropriateangles. For example, light redirecting means according to condition (1)may be any combination of transmissive or reflective, diffusive ornon-diffusive, and prismatic or textured layer. In addition, the lightredirecting means can be a diffraction grating, a hologram, or a binaryoptics layer.

[0233] A light redirecting means which redirects light in accordancewith condition (2) of Equation (13) is a specular reflector. Examples ofsuch a specular reflector can be a metallic coating (e.g., the lightreflector layer 222 in FIG. 20A can be a metallic coating), amulti-layer dielectric coating or a combination of these. In each case,the internal and external surfaces are preferably smooth and mutuallyparallel.

[0234] In FIG. 20A one of the preferred embodiments includes lightreflecting, redirecting means in the form of the reflector layer 222which reflects the light 220. The reflector layer 222 is disposedbeyond, or underiying, the first surface 208 of the base layer 206 andpreferably is a flat, specular reflector, such as a metallic coating.Also shown is an intervening layer 223 of index n₃ disposed between thebase layer 206 and the reflector layer 222. This intervening layer 223can be considered to be part of the base layer 206, or a separate layer,depending on the functional interaction between the base layer 206 andthe intervening layer 223. The index of refraction n₃ of thisintervening layer 223 can be adjusted to controllably affect theresulting spatial and angular distribution of the light 212 afterencountering the layer 223.

[0235] As can be seen, for example, in FIGS. 20B and 20C the lightredirecting layer 224 can be positioned at different locations, and eachlayer 224 can also have different characteristics enabling achievementof different light output characteristics as needed for a particularapplication. Further examples of light redirecting means and uses, aswell as specific embodiments, are illustrated in the remaining figuresand will be described in detail hereinafter.

[0236] In another embodiment of the polarized light luminaire system204, light converting means is included and is illustrated as apolarization converting layer 226 in FIGS. 21 and 22, for example. Inthese illustrated embodiments, the indices have n₄≧n₂ and the conditionsof Equation (9) must in general be met. In these embodiments, a lightconverting means includes a layer which changes at least part of onepolarization state (such as the light 220) to another polarization state(such as the light 218, or even light 227 of a third polarization state,which can be, for example, a combination of the first and second state).

[0237] The polarization converting layer 226 has the function ofchanging the polarization state to another state, such as rotatingpolarization by 90° (π/2). Moreover, such conversion is most preferablydone for oblique incidence. As one example we describe the nature ofsuch conversion for a uniaxial birefringent material where the index ofrefraction perpendicular to the optic axis is independent of direction.Many preferred materials, such as stretched fluoropolymer films are ofthis type. More general birefringent materials where the index ofrefraction is different in all directions can also be used following thegeneral methods described herein. To understand the polarizationconversion process, we first review the case for normal incidence.

[0238] As shown in FIG. 30E, a plate 229 of birefringent material hasits transverse axis along vector K and the optic axis is along vector I(see vectors in FIG. 30F). For a stretched birefringent film, thedirection of stretch would be along vector I. Vectors L J, K are anorthogonal triad of unit vectors along the x,y,z axes. For normalincidence, the wave normal is along vector K. We can describe thepolarization of the electromagnetic wave by its displacement vector D.Let D′ be the polarization of the ordinary ray, and D″ the polarizationof the extraordinary ray. Let n′ be the ordinary index of refraction,and let n″ be the extraordinary index of refraction. We can orient theoptic axis of the birefringent plate 229 so that it makes an angle of45° (π/4) to the incident polarization vector D₀. This vector has twocomponents D₀x=(1/{square root}2)D₀ cos ωt and D₀y=(1/{square root}2)D₀cos ωt. Upon emerging from the birefringent plate 229, the D vector hascomponents D₀x=(1/{square root}2)D₀ cos (ωt−δ″) and D₀y=(1/{squareroot}2)D₀ cos (ωt−δ′), where δ′=(2π/λ)n′h and δ″=(2π/λ)n″h, where h isthe plate thickness. Hence the phase difference introduced isδ′-δ″=|(2π/λ)(n″−n″)|h. In particular, if the emergent light haspolarization vector D at right angles to the intial polarization vectorD′, we need δ′-δ″=π (or more generally δ′-δ″=(2 m+1)π, where m is anyinteger). This means the thickness h should be chosen as h=|(2m+1)/(n″−n′) |λ/2.

[0239] In summary, we choose the thickness h in accordance with theabove relation and orient the optic axis at 45° to the incidentpolarization. In a preferred form of the invention such as in FIG. 26B,the light traverses the converting layer 226 birefringent plate 229twice, so that the actual thickness should be one-half of that specifiedabove. In other words, the thickness is the well known λ/4 plate. Anyreflections from a metallic mirror 231 introduces an additional phaseshift of approximately π to both components and does not change theconclusions.

[0240] In an embodiment wherein the light has oblique incidence with theconverting layer 226 (see FIG. 26B), it is first necessary to show thatsplitting of the incident beam into two beams (the well-knownbirefringent effect) does not cause difficulties. The reason this is nota problem is that the two beams emerge parallel to the initialdirection, but slightly displaced from one another. The two beams arecoherent with each other and the displacement is <λ. The angularsplitting is Δθ≈tan θ_(c)Δn /n where θ_(c) is the critical angle andΔn=(n″−n′),n=(n″+n′)/2. The displacement is ≈hΔθ/cos θ_(c)=hΔn/n tanθ_(c)/cos θ_(c). But, we will choose hΔn/cos θ≈λ/4, so automatically thedisplacement is <λ and the two light beams can be treated as one.

[0241] The geometry of oblique incidence on a uniaxial form of thebirefringent plate 229 is somewhat complicated, and thus to simplifymatters, we introduce the Eulerian angles as shown in FIG. 30F. Therelations between the (i,j,k) vector triad and the (I,J,K) ventor triadcan be read from Table 3. TABLE 3 I J K i −sin φ sin ψ + cos φ sin ψ +sin θ cos ψ cos θ cos φ cos ψ cos θ cos φ cos ψ j −sin φ cos ψ − cos φcos ψ − cos θ sin φ sin θ sin ψ cos φ cos θ sin ψ sin ψ k sin θ cos φsin θ sin φ cos θ

[0242] Let the normal to the air/plate interface =K, the direction ofthe incident wave normal =k, and the optic axis of the plate 229=I. Wewish to rotate the incident polarization D₀ by 90°. Since the incidentpolarization D₀ is in the interface plane, it is consistent to let D₀ bealong i₀ so that Ψ₀=π/2. The polarization D′ of the ordinary ray isperpendicular to both I and k. Therefore, let D′ be along i′. Nowi′_(x)=0. From Table 3 we conclude that tan Ψ′=cot φcos θ. Thepolarization of the extraordinary ray D″ is perpendicular to both D′ andk. Therefore, Ψ″=Ψ′±π2. We choose Ψ″=Ψ′−π/2, and then tan Ψ″=tan φ/cosθ. To achieve the desired output, we can appropriately orient thebirefringent plate 229. Just as in the normal incidence case, we let Ψ₀to be at 45° to the D′ and D″ directions. Therefore, we chose Ψ′=π/2,and then tan φ=cos θ. For a typical case, where θ is close to θ_(c)≈40°,φ≈37°. In practice, for a range of incidence angles and wavelengths onewould readily adjust φ experimentally to get the most completepolarization conversion, using the above formulae as a starting pointand guide. We next determine the thickness, h, of the birefringent plate229. As in the case of normal incidence, the condition is: h=|(2m+1)/(n″−n′)|λ/2. However, the extraordinary index of refraction n″ nowdepends on the angle of incidence θ and must be read off the indexellipsoid: (1/n′)² (1/n₀)² sin² θ+(1/n_(e))² cos² θ where n₀ is theordinary index of refraction and n_(e) is the extraordinary index ofrefraction. Also note that n′=n₀. Typically, the index of refractiondifferences are small, <0.1 and approximately, (n″−n′)≈(n_(e)−n_(c))cos² θ. In addition, the light path length for oblique incidence isgreater than that for normal incidence. The length h for obliqueincidence is greater than the thickness of the plate 229 by a factor of1/cos θ. Therefore, since the effective index difference is reduced bycos² θ, but the path length is increased by 1/cos θ, it follows that thethickness required for oblique incidence is larger than for normalincidence by 1/cos θ. In practice, for a range of incidence angles andwavelengths one would adjust h experimentally to obtain the mostcomplete polarization conversion. In practice, for a range of incidenceangels and wavelengths, one can adjust φ experimentally to obtain themost complete polarization conversion, using the above formulae as astarting point and guide.

[0243] In another example embodiment, the conversion of light of onepolarization into another polarization state can be considered asinvolving three steps: (1) separation of different polarization statesinto substantially distinct beams at every point on the system 204, (2)polarization conversion without affecting the desired polarization and(3) light diffusion into an appropriate angular distribution withoutdepolarization of the light output.

[0244] As described herein, a variety of methods can be used to separatethe different polarization states in the system 204. For example, thelow index layer 214 can be birefringent, as shown, for example, in FIGS.31A-C. The layer 214 can be, for example, an oriented fluoropolymerconvertor layer which creates two light beams 218 and 220 of orthogonalpolarization emerging from every point along the system 204. This can beused provided two conditions are met. The first condition requires thatthe birefringence of the layer 214 is large enough to significantlyprevent substantial overlap between the two polarized beams 218 and 220.This condition is summarized by Equations (15)-(17) where C is at least1 and preferably greater than 4. The second condition is that thedirection of birefringence orientation (direction of stretch) of thefirst layer 214 is substantially parallel to the y axis.

[0245] For φ=1-1.5 degrees, the birefringence must be at least 0.03-0.05to satisfy Equations (15)-(17). Measurements of the birefringence ofvarious commercial fluoropolymer films yielded the following data(average index, birefringence):

[0246] Tefzel 250 zh: (1.3961,0.054)

[0247] Tefzel 150 zm: (1.3979,0.046)

[0248] Teflon PFA 200 pm: (1.347,0.030)

[0249] The wedge layer 206 laminated with the 250zh material producedjust-separated polarized beams where even the Fresnel reflected partsdid not overlap.

[0250] In another embodiment, one can achieve even greater angularseparation of polarization by using a faceted redirecting layercomprised of a highly birefringent material.

[0251] A third approach for separation of polarization states uses asheet of polymeric beam splitters consisting of an alternating structureof birefringent/transparent layers 427 shown in FIGS. 30G and H. Such anarray of the layers 427 can rest on top of a collimated backlight 428and polarizes by selective total internal reflection. The index of thefilm of polymeric layers 429 parallel to the plane of light incidence islower than that of a transparent layer 430, and the index perpendicularto the plane of light incidence is closely matched to the transparentlayer 430, so that an incoming collimated light beam 431 from thebacklight 428 (inclined to the beam splitter layers 427) is split: theparallel polarized beam 431 is totally internally reflected, but theperpendicular component is transmitted.

[0252] One example of this arrangement can be Mylar/Lexan layers. Mylarindexes are: (1.62752,1.6398,1.486). The Lexan index is: 1.586. Thecomplement of the critical angle is twenty degrees; therefore, the beamsplitter layer 427 will function as long as the complement of theincidence angle is less than twenty degrees (in the Lexan). However, atglancing angles, Fresnel reflection causes reduction in the degree ofpolarization. For example, for thirteen degrees the Fresnel reflectedperpendicular component is 9%.

[0253] Another example of this arrangement of the layer 427 is uniaxialNylon/Lexan. Nylon indexes are: (1.568,1.529,1.498). Here there are twocritical angles, the complements of which are nine and nineteen degreesfor perpendicular and parallel, respectively. So, the obliquity must beinside this angular range for polarization to be operative. Taking thesame case for Fresnel reflection as for Mylar (thirtee degree angle),the Fresnel reflected perpendicular component is only 5%, because theindex matching is better.

[0254] For either of these examples, each beam splitter layer 427 needsto have the appropriate aspect ratio such that all rays of the beam 431have exactly one interaction with the film/Lexan interface.

[0255] In one embodiment, once the light of different polarizationstates is separated into two orthogonally polarized beams at everyposition along the backlight 428, there must be a means of convertingthe undesired polarization to the desired one, such as the polarizationconverting layer, 346 in FIG. 31C and 429 in FIG. 30G.

[0256] One method of performing the polarization conversion is by analternating waveplate combined with a lens or lens array. In the singlelens method, a light beam 218 and 220 will fall upon lenses focused totwo nonoverlapping strips of light of orthogonal polarization at thefocal plane. The alternating wave plate acts to rotate the polarizationof only one of the beams (220) by ninety degrees, the emergent lightwill be completely converted to light 218. This can be effected by thepresence of a half-wave retarder placed to capture only the light 220 ofone polarization. This has been demonstrated visually with a large lens,a plastic retardation plate, and Polaroid filters (Polaroid is aregistered trademark of Polaroid Corporation).

[0257] In a second approach using a lenticular array, one uses a thinsheet of lenses and an alternating waveplate structure (with thefrequency equal to the lens frequency), where the retardation changes by180 degrees for each lens. For a lenticular array 1 mm thick, each imagecan be of the order of 5 thousandth of an inch in size so theregistration of the lenticular array with the waveplate would have to beexact enough to prevent stack-up errors of less than one thousandth ofan inch.

[0258] Another method of performing the polarization conversion is byuse of a double Fresnel rhombus (“DFR”) which is another embodiment of aconverting layer, such as the layer 346 in FIG. 31C and 429 in FIG. 30G.The DFR avoids registration problems by selectively retarding accordingto angle instead of position. Such a DFR causes the light of firstpolarization state to suffer from total internal reflection eventscorresponding to 4×45°=180° of phase shift, while the other polarizationstate light is only transmitted, so that the output light is completelypolarized to the light of first polarization in one plane in the end.The DFR can be constructed, for example, by having four acrylic or Lexanfilms each embossed with 45 degree prisms, all nested. For the DFR tocause retardation the two orthogonal plane polarized beams L and R (by a¼-wave plate). If the L is transmitted by the DFR then the R beam willget converted to the L beam by the DFR. Finally the L beam is convertedto plane polarized by another ¼-wave plate, the orientation of whichdetermines the final plane of polarization.

[0259] In a preferred embodiment shown in FIG. 21A, the converting layer226 is disposed on the opposite side of the base layer 206 relative tothe polarization filter layer 216. In the embodiment of FIG. 21B, theconverting layer 226 is disposed on the same side as the polarizationfilter layer 216. As can be seen by reference to FIGS. 21A and B, theconverting layer 226 can even convert the light 218 and 220 to the lightof 227 of another third polarization state. This light 227 can be, forexample, the light of a third polarization state or even a variation on,or combinations of, the first or second polarization states discussedhereinbefore. The resulting light polarization is dependent on theresponse-characteristics of the converting layer 226. The convertinglayer 226 can therefore be designed to respond as needed to produce alight of desired output polarization state; and in combination withappropriate positioning of the layer 226, one can produce an outputlight in the desired direction having the required polarizationcharacteristics.

[0260] In another form of the invention illustrated in FIGS. 22A-E, theconverting layer 226 is utilized for other optical purposes. FIGS. 22,23, 24 E-F, 25-27, 28A and C, and 29 all illustrate use of theconverting layer 226 to change the light 220 of the second polarizationstate to the light 218 of the first polarization state. In addition, theelements of the luminaire system 204 are arranged such that the lightbeing processed will pass through, or at least encounter, one or more ofthe polarization filter layer 216 at least once after passing throughthe converting layer 216. For example, in the case of processing thelight 220, the arrangement of elements enables return of the light 220to pass through the polarization filter layer 216 after passing throughthe converting layer 226. In some instances, the light 220 can encounterthe polarization filter layer 216 two or more times before being outputas the light 218 of the first polarization state. FIGS. 22A-E illustrateexamples of a variety of constructions to achieve a desired output. InFIG. 22A, after the light 212 encounters the polarizing filter layer216, the reflected light 220 passes through the converting layer 226,and is converted to the light 218. The light is then returned to thepolarization filter layer 216 via internal reflection. In addition, inFIG. 22B, the light 220 also passes through the converting layer 226, isconverted to the light 218, and is then returned again to the filterlayer 216 after internal reflection. In these cases, n₃ is low enoughsuch that the relationship among n₁, n₂ and n₃ in Equation (10) is met.

[0261] In the embodiments of FIGS. 22C-E, a redirecting means in theform of the light reflector layer 222 is added to return the light 220to the polarization filter layer 216. As described hereinbefore for theembodiment of FIG. 20A, the intervening layer 223 has an index ofrefraction n₃ which can be adjusted to affect the spatial and angulardistribution of light encountering the layer 224. In a preferred form ofthe invention shown in FIGS. 22C-E, the layers of index n₂ and n₃ caninclude air gaps, and in the most preferred form of the invention thelayers of index n₂ are air gaps.

[0262] FIGS. 24A-F illustrate a sequence of constructions starting withuse of one of the polarization filter layer 216 in FIG. 24A andcontinuing construction of more complex forms of the luminaire system204. In FIGS. 24C-F, there is added one or more of the light redirectinglayer 224, at least one liquid crystal display (“LCD”) layer 230 andlight matching means, such as a matching layer 232. The matching meansacts to convert the light output by the assembly of the other layers toa particular polarization state preferred by a target device oradditional layer, such as the LCD layer 230. The matching layer 232 isthus a special case of the converting layer 226.

[0263] In FIGS. 23A-C are illustrated other forms of the polarized lightluminaire system 204 in combination with the LCD layer 230. In onegeneral form of the embodiment of FIG. 23A, a layer 234 is included. Inmore particular forms of the inventions, for example as in FIG. 23, thepreferred value of n₂ is about 1 (see, for example, FIGS. 23B and C). Incertain forms of FIG. 23A, n₂>1 can also be utilized. Alternatively,preferably choices for the relationship among indices of refraction areset forth in Equation (9) and (10).

[0264] Further examples of preferred embodiments are shown in FIGS. 26Aand B, and in FIG. 26A is included a cold cathode fluorescent tube(“CCFT”) light source 236. This embodiment further includes an angletransformer layer 238 which operates to change the angular distributionof the light. This angle transformer layer 238 can, for example, changethe distribution in the xz-plane to control the spatial uniformity oflight output from the device 10. In the preferred embodiment, thedistribution of the output light 250 is substantially uniform in itsspatial distribution over at least 90% of the output surface. Inaddition, the angular distribution of the light 212 in the xz-plane isapproximately ±θ max with respect to the normal to the back surface 211,where $\begin{matrix}{{\frac{\pi}{2} - \theta_{c} + {6\quad \Phi}} \geq \theta_{\max} \geq {\frac{\pi}{2} - \theta_{c}}} & (14)\end{matrix}$

[0265] and the back surface 211 is about perpendicular to at least oneof the first surface 208 and the second surface 210. The angletransformer layer 238 can be a tapered light-pipe section, a compoundparabolic concentrator (a “CPC”), a micro-prismatic film (FIG. 28C) aroughened-surface layer, or a hologram. The angle transformer layer 238is most preferably optically coupled to the base layer 206 without anintervening air gap. The angle transformer layer 238 can also operate tochange, and preferably narrow, the light distribution in the yz-plane toimprove brightness, LCD image quality, and viewer privacy as well. Inaddition, in FIG. 26A, an output diffuser layer 248 has been addedbefore the LCD layer 230 to broaden the angular distribution and enhanceuniformity of output light 242 provided to the LCD layer 230.

[0266] In another preferred embodiment of FIG. 26B, a CPC 239 is coupledto a light source 244 operating to help maintain output light 250 withinthe proper angular distribution in the xz plane. In addition, one cancontrol the range of angular output by use of a light redirecting means,such as a prismatic redirecting layer, such as the layer 246, using flatprismatic facets, such as the facets 247. See, for example, this type oflayer and prismatic facets in FIGS. 28C, D and E and FIGS. 29A and B andthe description in detail provided hereinafter. This embodiment as shownin FIG. 28E refers to the prismatic layer 251 and facets 253, and thisembodiment also adds after the LCD layer 302 a light diffuser layer 304for broadening light distribution in a specific plane. In a mostpreferred form of this embodiment, for example, shown in FIG. 28E, thelight 242 is directed-to pass through the LCD layer 302 within a narrowangular range in the xz-plane. The elements of the luminaire system 204are therefore constructed to assist in providing transmission of thelight 242 through the LCD layer 302 at an angle where the image formingproperties are optimized. With the diffuser layer 304 positioned on theother side of the LCD layer 302 relative to the base layer 206, thediffuser layer 304 can broaden the angular distribution of viewer outputlight 250 without diffusing the light 250 in the xy-plane. For example,the diffuser layer 304 can be a “parallel” diffuser which can take theform of a holographic diffuser or lenticular diffuser with groovessubstantially parallel to the y-axis. Viewers at a wide range of anglescan then see the image which is characteristic of the optimal angle forthe light 242 which is subsequently transmitted through the LCD layer302 to form the light 250. Example configurations utilizing this form ofgeneral construction are thus shown in FIGS. 28D and E and FIGS. 29A andB. Further, FIGS. 28D and E and FIG. 29A also include a transversediffuser layer 252 which diffuses the output light 242 provided to theLCD layer 302 only in the xy-plane in order to improve uniformitywithout broadening the distribution of the light 242 in the xz-plane.For example, the transverse diffuser 252 can be a holographic diffuseror a lenticular diffuser with grooves substantially parallel to thez-axis. Further details will be described hereinafter.

[0267] In FIGS. 27A and B are additional preferred embodiments whereinthe first layer means of index of refraction n₂ is most preferably notair. These embodiments show different examples of the light redirectinglayer 224. Further, in FIG. 27A medium 254 having index n₃ need not beair, but the various indices of the system 204 must meet therequirements of Equation (10) to achieve the total internal reflectionillustrated. In FIG. 27B the medium 254 is air, the light redirectinglayer 224 has curved facets 256, and the light 245 is focused within apreferred viewing zone 258.

[0268] The embodiments of FIGS. 28 and 29 preferably utilize an air gaplayer 260 as the first layer means. The layer 260 enables light to enterthe layer 260 after the light 212 has achieved an angle of incidenceless than the critical angle 3c characteristic of an interface betweenthe base layer 206 and the air gap layer 260. The embodiment of FIG. 28Bincludes a first redirecting layer 262 between the base layer 206 and adiffuser layer 264 and a second redirecting layer 265 on the other sideof the base layer 206. This first redirecting layer 262 includesrefracting/internally reflecting prisms 266 while the second redirectinglayer 265 includes refracting prisms 268. Two of the polarization filterlayer 216 are disposed either side of the base layer 206, eachtransmitting the appropriate light 218 or 220 which is passed throughthe associated light redirecting layer, 262 and 265, respectively. InFIG. 28C is a more preferred embodiment wherein the light redirectinglayer 246 comprises a refracting/internally reflecting layer having therelatively small prisms 247. The surface angles of each of the prisms247 can vary across the illustrated dimension of the redirecting layer246 in a manner described hereinbefore. This variation in angle enablesfocusing different cones of light coming from the prisms 247 onto thepreferred viewing zone 258 (see FIG. 27B). The light reflector layer 222can be a metallic coating as described hereinbefore.

[0269] The reflector layer 222 can be applied to the converting layer226 by conventional vacuum evaporation techniques or other suitablemethods. The other layers, such as the redirecting layer 246 can beformed by casting a transparent polymeric material directly onto thematching layer 232 (see FIGS. 24C-F and 28C and D). The polarizationfilter layer 216 can likewise be manufactured by conventional methods,such as deposition of multiple thin layers directly onto the base layer206. Also included is an angle transformer layer 274 coupled to the backsurface 211 (see FIG. 28C). This angle transformer 274 includes prisms276 which broaden the angular distribution of input light 212 to thebase layer 206 to help provide a more spatially uniform form of theoutput light 218 to the LCD layer 230. Other forms of the angletransformer layer 274 can be a roughened layer and a hologram (notshown) coupled to the back surface 211 (or other input surface) withoutan intervening air gap.

[0270] In the preferred embodiment of FIG. 28D, a first prismatic lightredirecting layer 249 is disposed between the base layer 206 and thepolarization filter layer 216. This redirecting layer 249 reduces theangle of incidence of light 280 incident on the polarization filterlayer 216. A second prismatic light redirecting layer 282 then redirectslight 284 output from the filter layer 216 to an LCD layer 302 with apost diffuser layer 304, operable as a parallel diffuser as describedhereinbefore. This embodiment further includes the CCFT light source 236with a reflector 290 having a position following at least a portion ofan involute of the light source 236 inner diameter. Another portion ofthe reflector 290 directly opposite the back surface 211 is convexlycurved or bent.

[0271] In the preferred embodiment of FIG. 28E a light redirecting layer251 comprises refracting micro prisms 253. A polarization filter layer296 is disposed adjacent a converting layer 298, and the transversediffuser layer 252 is positioned between the redirecting layer 251 andthe LCD layer 302. A parallel diffuser 304 is disposed on the lightoutput side of the LCD layer 302 with the light 242 directed through theLCD layer 302 at a preferred angle to optimize output light 301 for bestimage-forming quality of the LCD layer 302 (contrast, color fidelity andresponse time).

[0272] The embodiments of FIGS. 29A and B show some of the advantages ofsome forms of the invention over a conventional LCD polarizer system 304shown in FIG. 30A. In FIG. 30A, a prior art backlight 306 emits light308 of both polarizations in nearly equal proportions. A typical priorart LCD layer arrangement 310 includes a first form of polarizationfilter 312 and a second form of polarization filter 314 with the liquidcrystal layer 316 sandwiched therebetween. In this LCD layer arrangement310, the first polarization filter 312 must provide a high polarizationratio, that is, it must have an extremely low transmission of light ofthe second polarization state which is unwanted for input to the liquidcrystal layer 316 in order for the LCD layer arrangement 310 to provideadequate LCD contrast. In practice, the polarization filter 312 has ahigh optical density for the desired light of the first polarizationstate as well. The resulting losses therefore further degrade the LCDlight transmission and image output. In contrast to this prior artarrangement 310, the invention provides a much higher percentage oflight which is preferred by the LCD layer arrangement 316 thereby makinguse of a substantial portion of the light of the unwanted secondpolarization and also minimizing loss of the desired light of the firstpolarization state.

[0273] In the embodiment of FIG. 28A this advantageous processing of thelight 218 and the light 220 for the LCD layer 316 is accomplished bypositioning the converting layer 226 adjacent the base layer 206.Disposed adjacent the converting layer 226 is the polarization filterlayer 216. The light redirecting layer 224 includes curvedmicroprismatic facets 318 to broaden the angle of light distribution inthe xz plane and improve the uniformity of light distribution outputfrom the luminaire system 204. A transverse diffuser 320 is preferablylaminated to the light redirecting layer 224 or can be formed onopposite sides of a single polymeric layer (not shown). The polarizingfilter layer 216 can be laminated or is disposed directly onto theconverting layer 226 which in turn is laminated or deposited directlyonto the first surface 208.

[0274] In the preferred embodiment of FIG. 29A the advantageousprocessing of the light 218 and the light 220 for the LCD layer 302 isaccomplished by using a first polarization filter layer 324 and a secondpolarization filter layer 322. The first filter 324 can, however, have arelatively low polarization ratio compared to the prior art polarizationfilter 312. For example, the polarization filter layer 324 can have alower dye concentration than the prior art filter 312. This differenceenables higher LCD light transmission and improved image-formingproperties described hereinbefore. This preferred embodiment utilizes apost diffuser layer 328 which is coupled to an LCD system 330 (thecombination of the layer 324, the liquid crystal layer 302 and the layer322). Preferably the post diffuser layer 328 is laminated to, orintegrally formed with, the second polarization filter layer 322.

[0275] In the preferred embodiment of FIG. 29B, the advantages areachieved by using only one polarization filter layer 248 which resultsin reduced cost for the luminaire system 204 and increased lighttransmission. In this embodiment the light output through the matchinglayer 232 is preferably at least 90% composed of light 218 of the LCDpreferred polarization state. A coupled angle transformer 334 coupled tothe back surface 211 reduces the angular width of light distribution inthe yz plane, and this reduced angular distribution further improvesquality of the output light 250 making up the LCD image from theluminaire system 204.

[0276] In another preferred form of the invention shown in FIG. 33, thedevice 10 embodies a base layer 400 for receiving input light 402 from alight cavity 404 having lamp 406. The base layer 400 is most preferablyan acrylic wedge as explained hereinbefore. The input light 402 iscomprised of two polarization states “a” and “b” as shown in FIG. 33.The general terminology “a” and “b” is used throughout to cover alldifferent polarization combinations, such as linear “s” and “p”, leftand right circular, and elliptical polarization with the second statebeing orthogonal to the first. As described hereinafter the “a” and “b”states are preferably operated on by a polarization beam splitter,referred to hereinafter as interference layer 411 or reflectivepolarizer layer 480. Light 405 is thus output from the base layer 400into an air layer 407 under selected optical conditions in accordancewith requirements explained hereinbefore in detail. Some of the light405 with polarization “a” is further transmitted as light 409 into andthrough interference layer 411 disposed on glass plate 412, passesthrough air layer 414 and is acted upon by redirecting layer 416.Preferably this layer 416 is a prismatic layer described hereinbeforeand is used to control the angle of output of the light 409 ofpolarization state “a”. The redirecting layer 416 is designed preferablyto act on light centered at about 74° from the normal which is a typicalexit angle from the base layer 460, thereby changing the light directionto one substantially perpendicular to the particular exit face of thebase layer 400. This layer 416 can also be diffractive in nature such asa hologram layer in other embodiments. The output light 409 from theredirecting layer 416 can be further processed with post diffuser layers(not shown) and other appropriate layers described in great detailhereinbefore.

[0277] Regarding polarization splitting, two basic types of polarizationsplitting layers (the interference layer 411) were used. One type of thelayer 411 was based on vacuum deposition of thin inorganic films (forexample, an interference layer (or “polarization filter”) describedhereinbefore as alternating layesof high index n_(H) and low index n_(L)material, to create a polarization selective beam splitter which couldbe used in non-normal incidence, specifically in the neighborhood ofseventy-four degrees. Beam splitters of this type were created by vacuumdepositing the layers on 1 mm thick glass plate using standard thin filmphysical vapor deposition techniques.

[0278] The second type of the layer 411 used consisted of a multi-layerpolymer film. For example, the polymer film can be a well known DBEF (atrademark of 3M Co.) layer manufactured by 3M Co. Details concerningthis commercially available product can be found in PCT publicationWO95/17303 and WO96/19347. This film has the advantage that it could beused for normal incidence of the light as well as at wide incidenceangles, has a film defined polarization axis, and can potentially beproduced by high volume continuous manufacturing processes. Theseattributes allowed us to experiment with additional angles other thannormal incidence type systems or a narrowly defined oblique angle, andvarious orientations of the pass axis of the film.

[0279] There are a number of other well known approaches that canproduce polarization splitting effects used in these embodiments,including but not limited to scattering (such as dipole scattering),double refraction, reflection from collesteric liquid crystals, andthick film Brewster splitters.

[0280] As stated above, some of the light 405 has polarization state “b”and is reflected from the interference layer 411 (the polarizationsplitter) as light 418, passing through the air layer 411, the baselayer 400, air layer 420, a converting layer 422 (for example, a quarterwave plate layer), air layer 424 and is reflected by a reflector thatcould be a silver film, such as Silverlux (a trademark of 3M Co.) or adielectric reflector such as a BEF (a trademark of 3M Co.) type backreflector layer 426. This BEF layer 426 can also be disposed againstwhite paper 425 (shown in phantom) to diffusely reflect the small amountof light that has passed through the layer 426. The reflector layer 426may contribute to the polarization process or behave as a simplereflector. The reflected light 418 returns through the above-recitedlayers; but instead of being reflected by the interference layer 411,the light 418 has been converted by the converting layer 422 to light423 of polarization state “a” which is transmitted, and the output angleis controlled by the redirecting layer 416.

[0281] As noted above, the preferred polarization converting layer 422included commercially available quarter-wave stretched, birefringementpolymer films and were designed for 550 nm light wavelength at normalincidence. This form of converting medium was not necessarily the designoptium, but the materials were readily available; thus, many of theprototypes built used these available films at non-normal incidence andthe retardation was not strictly of the quarter-wave type. For example,many of the surfaces of the device 10 show various compensation effectsoff angle. The optimal compensation film to be paired with thesecomponents is not necessarily a quarter-wave type film oriented at 45°to the system symmetry axis as evaluated herein. However, theembodiments illustrate the operability of the basic designs of thedevices 10.

[0282] These films of the converting layer 422 were used in a number ofconfigurations. Since the film was supplied with adhesive, it waslaminated either to triacetate cellulose (“TAC”)film which had lowbirefringence when it was necessary to use it as a free “unlaminated”film. To reduce reflections, improve performance, and stability, manyarchitectures can be constructed where the film was directly laminatedto other components of the device 10.

[0283] Other light 423 of both polarization states “a” and “b” isreflected by top surface 432 of the base layer 400, then passes throughthe base layer 400, the air layer 420, the converting layer 422, the airlayer 424, and reflected by the BEF back reflector layer 426 backthrough the layers until striking the interference layer 411. This light423 therefore acts in a manner similar to the light 405 upon output fromthe base layer 400 producing an output light 434 of polarization state“a” and reflecting light 436 of polarization state “b”. This light 436also acts in the manner as the light 418 of polarization state “b”,resulting in output of light 438 of polarization state “a” (like thelight 428). It should be noted that throughout the specification onlycertain important example light ray paths are shown to illustrateoperation of the many embodiments of the device 10. To quantify theperformance of the devices 10 studied, a series of gain parameters weredeveloped which reflect increase of efficiency due to brightness andsolid angle changes. Therefore, the performance of the embodiment ofFIG. 33 is shown in Table 4 (the parameters are defined in the Example),and the measurement system and method are described in detail in theExample and in FIGS. 61-63.

[0284] The above-described device 10 therefore includes an assembly oflayers which act as a “cavity” containing an internal polarizationconversion and recycling mechanism. The term “cavity” can include, forexample, a light waveguide wherein the light is moving between layers.Due to the “cavity” or waveguide nature of the device 10, the light raypaths can be numerous in type and combination. The requirement is thatthere be sufficient polarization conversion in the cavity so that lightis converted from the state “b”, which preferentially reflects from theinterference layer 411, to the state “a” which is transmittedefficiently to avoid substantial internal losses. Consequently, multipleFresnel reflections and non-ideal conversion mechanisms from “b” to “a”states within the cavity are permissible. TABLE 4 Comparison of VariousArchitectures to Basic Tapered Luminare with a Metallic Based BackReflector g Total (Usable Redirecting Base g Luminance g RangeGain-product of Layer Layer Back Reflective (Brightness (Rangebrightness gain FIG. Display Side Diffuser (B. Layer) ReflectorPolarizer Rotator Gain) Gain) and range gain) 33 Yes No SmoothStructured Evaporated Yes 1.04 1.26 1.31 34 Yes No Smooth StructuredEvaporated No 1.06 1.20 1.27 35 Yes No Smooth Structured None No 1.071.09 1.17 36 Yes No Smooth Metallic Evaporated Lam to BRefl 1.12 1.211.35 37 Yes No Smooth Metallic Evap on Pipe Lam to BRefl 1.10 1.06 1.1738 Yes No Smooth Metallic None None 1.00 1.00 1.00 39 Yes No SmoothMetallic Evaporated Lam to Pipe 1.16 1.12 1.30 40 Yes No Smooth MetallicNone Lam to Pipe 0.97 1.02 .99 45 Yes No Smooth Structured EvaporatedLam to Pipe 1.13 1.19 1.35 46 Yes No Smooth Structured None Lam to Pipe1.06 1.11 1.18 47 Yes No Smooth Structured At Pipe Input None 1.16 0.991.15 48 Yes No Smooth Structured At Pipe Input At Pipe Input 1.08 1.011.09

[0285] To investigate the polarization conversion mechanisms in thedevice 10, a variety of components were evaluated regarding convertinglight in TE(s) and TM(p) states, and 45° incident linear polarization ofthe light into the orthogonal linear polarization state. To make thismeasurement a 623.8 nm laser and a polarizer analyzer pair were used.Each sample was illuminated at seventy-four degrees incidence which isnear the center of the ray distribution leaving the base layer 400. Forthe prismatic form of the redirecting film 414, transmitted light wasmeasured, and for all other parts reflected light was measured. Theresults in Table 5 illustrate these conversion effects. TABLE 5 SystemTE TM 45° BEF Only 17% 18% 30% BEF and Separate Converter 27% 35% 56%BEF with Laminated Converter 29% 39% 42% Metallic Reflector Only 0% 0%29% Metallic Reflector with Separate Converter 35% 37% 49% MetallicReflector with Laminated Converter 52% 59% 33% Light Pipe, Specular 1%6% 69% Prismatic Redirecting Film 2% 5% 54%

[0286] Generally, conversion of light in a light pipe type of geometrycan originate from a number of mechanisms and that the effect of thevarious interactions in the system depends on the specific polarizationstate at that point, for example, TE, TM, 45°, circular, etc. Hence, thepolarization conversion effect can result, for example, from totalinternal reflection, reflection beyond the Brewster's angle fromdielectric interfaces, and material birefringence.

[0287] Since every transmission or reflection has the potential ofchanging polarization depending on the exact circumstances, there are avariety of ways that compensation/polarization conversion films can beused to advantageously improve performance by increasing the conversionand specifically control polarization beyond the natural effect ofvarious elements. In addition, the angle of the polarization splittinglayer can be used as an important parameter to enhance polarizationconversion in the manner intended.

[0288] Example architectures chosen to study were either (1) the centralrays of the luminaire of TE or TM polarization with respect to thesystem which makes the base layer 400 and redirecting layer 414 have lowconversion and have good control over the polarization, or (2) at 45°where nearly every interaction converts polarization, and the net effectof all of the separate conversions is some total amount of conversion ordepolarization of the light recycles through the polarization cavity. Italso should be readily understood that one can control the lightpolarization conversion process in the 45° architecture, as is done inother cases.

[0289] In an additional embodiment of the invention shown in FIG. 34,the layer structure is like that of the embodiment of FIG. 33 except theconverting layer 422 is removed. The polarization recycling cavity isstill substantially formed by the combination of the interference layer411 and the back reflector layer 426. As a result of removing theconverting layer 422, the light 418 of polarization “b” is transmittedthrough the base layer 400, the air layer 420 and is reflected as light440 of polarization “b” and “a”, with some of the “b” state beingconverted to the “a” state. Polarization conversion now relies onconversion from reflections from the various elements, such as the backreflector layer 426 and residual birefringence of the various layers ofthe device 10 to output light 442 preferably of polarization state “a”.The performance of this embodiment is shown in Table 4.

[0290] In a further embodiment in FIG. 35, the converting layer 422 andthe interference layer 440 have been removed as compared to theembodiment of FIG. 33. This embodiment includes an unpolarized form ofthe light 402 input from the lamp cavity 404. This embodiment thus showsa polarization level of only about 6% above random with a highbrightness direction being along the direction of propagation of thelight in the base layer 400. The performance of this embodiment is shownin Table 4.

[0291] In another preferred embodiment shown in FIG. 36, the arrangementof layers is quite similar to the embodiment of FIG. 33 and generallyresults in processing the same family of light rays of particularpolarization with the various polarization cavity elements. Theprincipal distinction is the reflector layer is now a metallic backreflector layer 446 which is laminated to the converting layer 422 withno intervening air layer. Preferably this layer 446 comprises acommercially available, silver coated polymer film (Silverlux, forexample, referred to hereinbefore) laminated to a substrate, such asaluminum or other suitable support. The performance of this embodimentis shown in Table 4.

[0292] In an additional preferred embodiment shown in FIG. 37, thearrangement is quite similar to the embodiment of FIG. 36 except thepolarization splitting interference layer 411 is directly disposed ontothe base layer 400. This layer 411 is preferably deposited byevaporation although any other conventional thin film depositiontechnique can be used to produce an operative layer. This layer 411 canalso be obtained by lamination of reflective polymers or otherpolarization splitter layers which are of low loss and do notsignificantly attenuate light rays in the base layer 400. The relativeperformance of this embodiment is illustrated in Table 4.

[0293] In yet another embodiment shown in FIG. 38, the arrangement oflayers is quite similar to that of FIG. 35 except the back reflectorlayer is the metallic back reflector layer 446. The light ray paths arealso quite similar to those in FIG. 35. The degree of polarization isabout 4% which is also very similar to the device 10 of FIG. 35. Theperformance of this embodiment of FIG. 38 is shown in Table 4.

[0294] In yet a further preferred embodiment in FIG. 39, the arrangementof layers is similar to that of FIG. 36 except that the converting layer422 is laminated to the base layer 400 instead of being laminated to themetallic back reflector layer 446. Instead, there is an air layer 448between the converting layer 422 and the metallic back reflector layer446. The light ray paths are also quite similar to those of FIG. 36,except that additional polarization of unpolarized light occurs andpolarization conversion also occurs before the light exits the baselayer 400. These additional polarization and conversion steps will bedescribed hereinafter in reference to the embodiment of FIG. 40. Theresulting output is light 452 suitably controlled in angle by theredirecting layer 416. A portion of the light 450 has been reflected bythe interference layer 411 as light 453 of polarization state “b” whichis further processed and converted to the light 438 of state “a”, andoutput. The performance of this embodiment of FIG. 39 is shown in Table4.

[0295] In a yet another preferred embodiment in FIG. 40, a differentpolarization recycling and conversion arrangement is shown. In thisembodiment, the polarization recycling cavity is formed by the baselayer 400 and a laminated form of the converting layer 422 whichconfines light by total internal reflection (hereinafter, “TIR”). Inthis device 10, the input light 402 is continuously converted inpolarization by the converting layer 422 as the light 402 travels downthe diminishing thickness of the wedge shaped base layer 400. Thesecomponents of the light 402 which are p-polarized (“a” state for thisembodiment) with respect to the top surface 432 are then preferentiallycoupled from the base layer 400 due to the lower reflectivity of the“a”, state light as compared to s-polarized (“b” state); and as thelight ray angles pass θ_(c) (see discussion hereinbefore concerningcritical angle), the light 402 begins to escape the base layer 400.Various example light ray paths are shown in the figure. In one case,the light 402 of polarization “a” and “b” is reflected from the topsurface 432 and bottom surface 454 until θ_(c) has been achieved. Thelight 456 of polarization “a” is then output through the air layer 407and through the redirecting layer 416 with a controlled angular rangetoward the viewer. A remaining component of light 458 of polarizationstate “b” is reflected and passes through the base layer 400, and thelight 458 is coupled out into the converting layer 422. Upon reflectionand traversal again of the layer 422, the light 458 has become light 460of polarization state “a” and is output through the air layer 407 andthe redirecting layer 416. A further example of the process is the light458 passes once through the converting layer 422, is outcoupled into airlayer 448, reflected by the metallic reflector layer 446, passes againthrough the converting layer 422 to become light 462 of polarization “a”which is then output toward the viewer. The generally preferred outputis still, however, light of “a” polarization. Therefore, the differencebetween the reflectivities of the “a” and “b” states enables improvedpolarization efficiency. In addition, the resulting polarizationproduced was about thirteen percent. The performance of this embodimentis shown in Table 4.

[0296] In yet another embodiment shown in FIG. 41, the arrangement oflayers is similar to FIG. 40, but the limited difference betweenreflectivities of the “a” and “b” states are further enhanced bydepositing a polarization splitting layer 464 directly onto the topsurface 432 of the base layer 400.

[0297] In another variation related to the embodiments of FIGS. 40 and41, FIG. 42 shows a back reflector layer 466 directly coupled to theconverting layer 422 which is also laminated to the bottom surface layer454 of the base layer 400.

[0298] In yet another embodiment shown in FIG. 43, the converting layer422 can be disposed on the other side of the base layer 400 above thetop surface 432. This arrangement also accomplishes the purpose ofconfining the light as it travels along the base layer 400. Severalexample light ray paths are shown with the primary difference being thelight 402 of polarization state “a” and “b” is outcoupled from the topsurface 432, and then the “b” state component is converted to light 468of “a” state by the quarter wave plate converting layer 422.

[0299] In a further variation on the embodiment of FIG. 43, the baselayer 400 in FIG. 44 is made of a birefringement polarization convertingmaterial which functionally operates to include with the base layer 400the polarization converting function of the converting layer 422 of FIG.43. As shown in FIG. 44, the light 402 is outcoupled into the air layer407 as the light 468 of polarization state “a”.

[0300] In considering the performance measurements in Table 4, it wasnoted that increased polarization efficiency did not necessarily resultin systematic gain increase. This was believed to arise from scatteringand absorption losses from the type and quality of the adhesive bondused to couple various layers and also on the attached quarter wavefilm.

[0301] In a further variation on the embodiment of FIG. 39, the backreflector layer in FIG. 45 is the BEF type back reflector layer 426rather than the metallic back reflector 446. The light ray paths betweenlayers are quite similar, and the performance is shown in Table 4.

[0302] In a further variation on the embodiment of FIG. 40, the backreflector layer in FIG. 46 is the BEF type back reflector layer 426rather than the metallic back reflector 446. The light ray paths arequite similar, and the performance is shown in Table 4.

[0303] Another form of the invention is shown in FIG. 47, in which apolarization splitting layer 470 is disposed at the input to the baselayer 400. In this embodiment, the polarization recycling “cavity” isformed by the lamp cavity 404 and the polarization splitting layer 470.The input light 402 thus is processed by the light cavity 404 and thepolarization splitting layer 470 to produce light 476 of polarizationstate “a”. In order to achieve this result, the polarization splittinglayer 470 most preferably is positioned to have its pass axis eithersubstantially parallel, or perpendicular to the direction of thesymmetry axis of the base layer 400. This arrangement keeps light in thebase layer 400 substantially in one polarization state as it travelsdown the base layer 400. Therefore, the input light 402 (the lightemitted by the lamp 406), leaves the lamp 406 in an unpolarized stateand ultimately encounters the polarization splitting layer 470. Asubstantial part of the light 402 is transmitted as light 476 ofpolarization state “a”, while the remainder of polarization state “b” isreflected or recycled back into the lamp cavity 404 for eventualconversion and output as the light 476 of polarization “a”. Theperformance of this device 10 is shown in Table 4.

[0304] In a variation on the embodiment of FIG. 47, the arrangement ofFIG. 48 further includes the feature of a polarization converting layer478 on the lamp cavity side of the polarization splitting layer 470. Thelight ray paths in this embodiment are quite similar to the paths shownin FIG. 46. The performance results are shown in Table 4.

[0305] In another variation on the embodiment of FIG. 33, the device 10of FIG. 49 does not include the redirecting layer 416, the base layer400 is a textured light pipe, rather than one having optically smoothsurfaces, and a film based reflective polarizer layer 480 is substitutedfor the interference layer 410 to split and reflect the lightpolarization states. The effect of the texture on (or equivalentlywithin) the base layer 400 is to diffuse (or misdirect) the light 402 asit travels down the base layer 400 and also as it exits and is recycledthrough the base layer 400. The textured base layer 400 can, forexample, be created by spraying a curable coating onto a smooth versionof the base layer 400 or by using a textured mold to create the texturedform of the base layer 400, or by dispersing submicron to micron sizescattering centers within the layer 400. These textures operate suchthat any ray path undergoes small misdirection. This interaction involesa weak scattering event and while changed by this, the ray path is notchanged drastically. In this context, the texture refers either to slopevariations on its surface of the base layer 400 or refractive indexvariations on or within the base layer 400, either of which will deviatethe ray path by an amount on the order of fractions of a degree todegrees from its path in the absence of such texture. This embodimentwas directed to evaluation of the losses arising from the redirectinglayer 416 processing broad angle illumination provided by thepolarization elements of the device 10. As can be noted by reference toTable 6, the elimination of the redirecting layer 416 results inimproved efficiency. The light ray paths followed are quite similar tothe paths in FIG. 33 except the light rays exit the device 10 at widerangles without use of the redirecting layer 416.

[0306] In another form of the embodiment of FIG. 49, the device 10 ofFIG. 50 does not include the textured form of the base layer 400described previously. The comparative performance is shown in Table 6,and the light my paths are quite similar to that of FIG. 49. It shouldbe noted that the data of Tables 4 and 6 cannot directly be comparedbecause a different reference architecture was used in each table. Onecan roughly compare the data of one table to another by multiplying thedata of Table 4 by 1.17 to compare with Table 6 data

[0307] In another form of the embodiment of FIG. 49, the device 10 ofFIG. 51 uses the metallic back reflector 446 rather than the BEF-typeback reflector layer 426. In addition, the layer 426 is laminated to theconverting layer 422 without an air layer. The light ray paths are quitesimilar to those in FIG. 49, and the comparative performance is shown inTable 6.

[0308] In a variation on the embodiment of FIG. 51, the device 10 ofFIG. 52 does not use a textured form of the base layer 400. The lightray paths are very similar, and the comparative performance is shown inTable 6.

[0309] In another form of the embodiment of FIG. 33, the device 10 ofFIG. 53 uses the reflective polarizer layer 480 rather than theinterference layer 411; and a textured form of the base layer 400 isused. The light ray paths are quite similar, and the comparativeperformance is illustrated in Table 6.

[0310] In another form of the invention shown in FIG. 54 the device 10is similar to the one shown in FIG. 53 except the redirecting layer 416is switched with the reflective polarizer layer 480 (a polarizationsplitter like the interference layer 411). As a result of thisrearrangement, the light ray paths are quite TABLE 6 Comparison ofVarious Architectures to Basic Tapered Luminare with a Structured BackReflector. Base g Luminance g Range g Total Redirecting Layer BackReflective (Btightness (Range (Usable FIG. Layer (B. Layer) ReflectorPolarizer Rotator Gain) Gain) Gain) 49 No Textured Structured Over B.Layer Under B. Layer 0.71 1.92 1.37 50 No Smooth Structured Over B.Layer Under B. Layer 0.68 2.02 1.38 51 No Textured Specular Over B.Layer Under B. Layer 0.67 2.41 1.62 52 No Smooth Specular Over B. LayerUnder B. Layer 0.77 2.36 1.81 53 Yes Textured Structured Over B. LayerUnder B. Layer 1.10 1.09 1.2 54 Yes Textured Structured Over Nfilm UnderB. Layer 0.97 1.13 1.1 55 Yes Textured Structured Over B. Layer UnderRefle 0.96 1.16 1.11 56 Yes Textured Structured Over B. Layer Laminatedto 1.06 1.14 1.21 57 Yes Textured Structured None None 1.00 1.00 1.00 58Yes & Textured Structured Over Dfilm @ None 1.08 1.1 1.19 Dfilm 45 59Yes & Textured Structured Over Nfilm @ None 1.04 1.08 1.12 Dfilm 45 60Yes & Textured Structured Over Wedge @ None 1.15 1.09 1.25 Dfilm 45

[0311] different. The input light 402 to the base layer 400 can, as inthe embodiment of FIG. 53, be coupled out through the top surface 432 ofthe base layer 400 with some of the light 405 of polarization “a” outputthrough the redirecting layer 416 and the reflective polarizer layer480. Some of the light 405 of polarization state “b” is reflected aslight 482, passing through the base layer 400, the air layer 420, theconverting layer 422, the air-layer 424 and is reflected by the BEF typeback reflector layer 426. Upon return passage through the convertinglayer 422, the light 482 changes to light 484 of polarization state “a”and output to the viewer through the base layer 400, the redirectinglayer 416 and the reflective polarizer layer 480. The exchanged positionof the redirecting layer 416 and the reflective polarizer layer 480 alsoresults in the redirecting layer 416 operating on wide angle lighttraveling in both the forward and reverse directions as shown in FIG.54. The forward traveling light passes through the base layer 400 in amanner like that shown in FIG. 52, but the reverse traveling lightpasses backward through the base layer 400. Ultimately, some of thislight will even recycle through the lamp cavity 409. Several exampleoverlapping light paths are illustrated in FIG. 54, but numerous otherlight paths also exist The performance of this device 10 is shown inTable 6.

[0312] In another variation on the embodiment of FIG. 53, the device 10in FIG. 55 places the converting layer 422 above the base layer 400. Thelight ray paths are similar to those of FIG. 53 except the polarizationconversion occurs above the base layer 400. For example, the light 402is coupled out of the top surface 432 as the light 405 passes throughthe converting layer 422 to reverse polarization states, and the light409 of polarization state “a” is output through the reflective polarizerlayer 480 and the redirecting layer 416. Of more interest is light 482of polarization state “b” reflected by the reflective polarizer layer480 which passes through the air layer 407, the converting layer 422,the air layer 485, the base layer 400, the air layer 420, reflected bythe BEF type back reflector layer 426 and returns through these layersto be converted by the converting layer 422 to light 484 of polarizationstate “a” for output. The comparative performance of the device 10 isshown in Table 6.

[0313] In another variation on the embodiment of FIG. 53, the device 10of FIG. 56 has the converting layer 422 laminated to the base layer 400.The light ray paths are thus quite similar, and the performance of thisembodiment is shown in Table 6.

[0314] In another form of the embodiment of FIG. 35, the device 10 ofFIG. 57 uses a textured form of the base layer 400. The light ray pathsare quite similar and the performance is shown in Table 6.

[0315] In another form of the invention illustrated in FIGS. 58-60,operation of the device 10 as a polarized luminaire is shown without useof a separate form of the converting layer 422. This is accomplished bylight reflection past the Brewster angle, polarization conversion uponoff-angle metallic reflection events, polarization due to total internalreflection and internal birefringence in a stretched film base layer ofthe primitive redirecting layer 416 and the BEF type back reflectorlayer 426. Each of these mechanisms can contribute to polarizationconversion when we position the reflective polarizer layer 480 at thesame angle to the symmetry axis of the device 10. For simplicity, a 45°angle is chosen for the pass axis of the polarizer layer 480.

[0316] In FIG. 58 is shown the device 10 having substantiallyunpolarized light 486 traveling along the base layer 400 until its angleincreases to exceed θ_(c) at one of the top surface 432 or the bottomsurface 457. The light 486 then passes through the air layer 407, theprismatic redirecting layer 416 which changes the angle of the light486; and after passing through air layer 487, anotherredirecting/diffuser layer 488 broadens die angular distribution of thelight 486. The light 486 then passes through air layer 489 andencounters a reflective polarizer layer 490 which acts as a polarizationsplitting layer. This polarizer layer 490 is oriented so that thepass-axis is at 45° to the symmetry axis of the device 10 which in thisparticular case is the primary propagation direction of the device 10.The polarizer layer 490 splits the light 486 into two components: light492 of one state “a” is preferably passed and light 494 of state “b” ispreferably reflected. The light 494 is thus recycled back in a broadangular distribution by passing through the redirecting/diffuser layer488. This broad angular distribution of the light 494 has a variety ofrecycling paths. For example, some of the light 494 will recycle throughthe redirecting/diffuser layer 488 in the general manner shown in FIG.54. Polarization conversion in this case can occur by interactionthrough Fresnel reflection from the faces of the base layer 400, totalinternal reflections in the redirecting/diffuser layer 488, conversiondue to birefringence in the redirecting/diffuser layer 488, metallicreflection effects and diffuse scattering in the lamp cavity 404. Thelight 494 traveling this path can ultimately recouple through theredirecting/diffuser layer 488 and back through the other components ofthe device 10. The wide variety of recycled rays ultimately reach thepolarizer layer 490 with some polarization conversion accumulatedresulting in system gain. The performance of this device 10 is shown inTable 6.

[0317] In a variation on the embodiments of FIG. 58, the device 10 inFIG. 59 has the polarizer layer 490 positioned below theredirecting/diffuser layer 488 so that light rays recycle in the generalmanner similar to those in the embodiment of FIG. 54 without the broadangle diffusion effects present in the embodiment of FIG. 58. Thisembodiment in FIG. 59 also takes advantage of off-angle reflections andscattering to convert polarization state of the light 486 rather thanthe explicit polarization converting layer 422 of FIG. 54. Theperformance of this embodiment is shown in Table 6.

[0318] In another embodiment similar to that of FIG. 53, the device 10of FIG. 60 accomplishes polarization conversion by off-angle reflectionssince the reflective polarizer layer 480 is at a 45° angle relative tothe symmetry axis of the device 10. The device 10 thus does not includethe converting layer 422 and does add the redirecting/diffuser layer 488with an intervening air layer 491. The performance of this device 10 isshown in Table 6.

[0319] Birefringent Layers in Luminaire Systems

[0320] A birefringent material can be used to advantage in the polarizedlight luminaire system 204 discussed hereinbefore. In the embodimentillustrated in FIG. 31A, the first layer 214 can be a birefringentmaterial of index n₂ with two different optical indices n_(2α) andn_(2β) for the light 212 of two different polarization states “a” and“b”, both indices being less than one. This light 212 encounters thelayer 214 near the respective critical angles for these two polarizationstates,

θ_(cα)=arcsin (n _(2α) /n ₁)  (15)

and

θ_(cβ.)=arcsin (n _(2β) /n ₁)  (16)

[0321] The conditions of Equation (10) must be satisfied for n₂ equal toboth n_(2α) and n_(2β), independently. The light 212 of bothpolarization states decreases its angle of incidence by an angle 2Φ foreach cyclic reflection from the first surface 208 and the second surface210 as described previously. In this embodiment n_(2α)>n_(2β) andtherefore θ_(cα)>θ_(cβ). As the incidence angle for both polarizationstates decreases, the light 212 of both polarization states canencounter the interface with the birefringent first layer 214 with thelight having an incidence angle less than the first critical angleθ_(cα), but exceeding the second critical angle θ_(cβ). Therefore, light218 of the first polarization state is at least partially transmittedthrough the birefringent first layer 214, while the light 220 of thesecond state is preferentially reflected by total internal reflection.This reflected second-state light 220 and the residual first-state light218 continue to decrease their angles of incidence with successivereflections. The light 218 of the first polarization state istransmitted at each successive encounter with the interface between thefirst layer 214 and the base layer 206. The light 220 of the secondstate continues to undergo total internal reflection at this interfaceuntil its angle of incidence becomes less than the second critical angleθcβ, at which point this second-state light 220 also is at leastartially transmitted through the birefringent first layer 214. By virtueof this mechanism and of the difference in indices n_(2α) and n_(2β),the light exiting the birefringent first layer 214 has a different angledistribution for the two polarization states “a” and “b”.

[0322] Birefringent materials can in general include crystallinematerials having an anisotropic index of refraction. A preferredmaterial is a stretched polymeric film such as stretched fluorinatedfilm. The stretching orients the film and makes the index of refractiondifferent along that direction. Elsewhere we give birefringence valuesof these stretched fluoropolymer film with Δn ranging from 0.030-0.054.Other films are PVA (Polyvinylalcohol). Polypropylene, Polyolefin oreven Polyester (Mylar). Mylar is actually biaxial, but may still be usedto rotate polarization. More traditional uniaxial birefringent materialsare: Calcite and Quartz. These are not as practical as the stretchedfilms. In practice the two polarization states are well-separated onlyif the two indices are sufficiently different. This condition may beexpressed as,

θ_(cα)≧θ_(cβ) sφ  (17)

[0323] where s must be at least 1 and is preferably greater than four.This condition may be achieved, for example, using uniaxially orientedfluoropolymer material for the birefringent layer, acrylic polymer forthe base layer 206 and reasonable values of 101 (between one andone-and-a-half degrees is typical for notebook computer LCDbacklighting).

[0324]FIG. 31B is like FIG. 31A, but the redirecting layer 224 has beenadded; and the preferred embodiment uses air for the layer 207 havingindex n₃. The light 218 and the light 220 are output from the system 204at different angles.

[0325]FIG. 31C illustrates another variation on FIGS. 31A and B, but theredirecting layer 224 comprises a flat faceted reflective layer 340. Thelight 218 and also the light 220 are directed to a converting layer 346which transmits the light 218 without substantially changing itspolarization state; however, the converting layer 346 does convert thelight 220 to the light 218 of the desired first polarization state. Theconverting layer 346 shown in FIG. 31C has a construction that operatesto convert the light polarization only within the angular range occupiedby the light 220. The converting layer 346 thus utilizes theschematically illustrated angular separation of the light 218 and thelight 220 to carry out the conversion of the light 220 to the light 218without converting the light 218 to the light 220.

[0326] In the embodiments of FIGS. 31D and E, the reflected form of thelight 220 is returned to the interface of the base layer 206 with thebirefringent first layer 214. This is accomplished by virtue of totalinternal reflection of the light 220 together with passing at leasttwice through the converting layer 346, which results in at leastpartially converting the light 220 into the light 218 of the firstpolarization state. Since this light 218 has an incidence angle lessthan the first critical angle θ_(cα), the light 218 is transmittedthrough the interface between the base layer 206 and the first layer214. This light 218 can then be reflected or transmitted by theredirecting layer 224, depending on the particular nature of theredirecting layer 224. The alternatives of transmitted and reflectedlight are shown in phantom in FIGS. 31D and E. Further, in theembodiment of FIG. 31D, the converting layer 346 is on the same side ofthe base layer 206 as the birefringent first layer 214. The convertinglayer 346 is also disposed between the base layer 206 and thebirefringent first layer 214. The embodiment of FIG. 31E shows anothervariation on FIG. 31D with the converting layer 226 and the birefringentfirst layer disposed on opposite sides of the base layer 206.

[0327] In the embodiment of FIG. 31F the system 204 is similar to theembodiment of FIG. 31D, but the redirecting layer 224 comprises a layerof facets 311. In the embodiment of FIG. 31G, the system 204 furtherincludes the LCD layer 302, the matching layer 232, and the diffuserlayer 304 is disposed in a spatial position after the light 218 haspassed through the LCD layer 302. The redirecting layer 224 comprisesthe layer of microprisms 251 having flat faces and a metallic coating342 for high light reflectivity. Also shown is the angle transformerlayer 238 to control the spatial distribution of the light 253 outputfrom the system 204. The embodiment of FIG. 31H is similar to theembodiment in FIG. 31G, but the system 204 uses curved facets 345 forthe redirecting layer 224 with facet angles adjusted at differentspatial locations to focus the output light 250 onto a preferred viewingzone. The angle transformer 238 is illustrated as a CPC.

[0328] Light Diffuser After LCD Layer Processing

[0329] In the embodiments shown in FIGS. 12N and 12O the LCD display 216or 236 provides an output light to the viewer. In a further improvementof these embodiments a post diffuser layer 350 is disposed in the pathof the light 250 output from the LCD layer 302 (see FIGS. 32A and B). Inthe preferred embodiments shown in these figures, the general operationis similar to the embodiments illustrated in FIGS. 26B, 28D and E; 29Aand B and 31G, but without any of the polarization filter layers 216. Asdescribed hereinbefore, it is advantageous to provide light to the LCDlayer 302 in a collimated angular range, preferably substantiallyperpendicular to the LCD layer 302 to optimize the image outputtherefrom. The use of the post diffuser layer 350 allows the outputlight 253 to provide an image to viewers over a wide angular rangewithout compromising light contrast and color fidelity.

[0330] One aspect which is preferably controlled in a system includingthe post diffuser layer 350 is the width in the xz-plane of the angulardistribution transmitted through the LCD layer 302. The output angulardistribution preferably has a full width less than $\begin{matrix}{{\Delta \quad \theta_{\rho \quad d}} = {2{n_{l\quad {cd}}\left( \frac{1}{d} \right)}}} & (18)\end{matrix}$

[0331] and a full width less than half of this value is even morepreferred. In this equation Δθ_(pd) is in radians, n_(LCD) is theaverage index within the LCD layer 302, □ is the repetition period ofdisplay pixel rows in the z-direction, and d is the thickness of the LCDlayer 302. For a typical LCD used in notebook computers, n_(LCD) isapproximately 1.5, l=0.3 mm, and d=3 mm. For this example, Δθ_(pd) ispreferably less than 18 degrees, and a full-width of nine degrees orless is even more preferred. By comparison, Equation (8) can be used tocalculate the output angular width of the current invention using aflat-facet prismatic redirecting layer, such as is shown in FIG. 32A(layer 359) or in FIG. 28B (layer 262). For a typical notebook computerbacklighting system, Φ=1.3 degrees and n=1.49. In this example, Equation(8) gives an output angular distribution of eighteen degrees.

[0332]FIG. 32A shows a preferred arrangement of the system 204 having aparallel form of the post diffuser 350 disposed overlying the LCD layer302. Also included is a holographic angle transformer 364 disposed onthe back surface 211.

[0333] In another embodiment shown in FIG. 32B a refracting/internallyreflecting layer 360 includes curved facets 362 in order to narrow theangular distribution in the xz-plane of light 364 directed through theLCD layer 302, and thereby to improve image quality by reducing parallaxat the post diffuser layer 350. The embodiment has the curved reflectingfacets 362, but flat refracting facets can achieve the desired functionas well, as shown in FIG. 32C. In either case, the curved facets 362preferably have a focal length less than the repetition period betweeneach of the facets 362. The angular distribution in the xz-plane ispreferably narrowed beyond the width given in Equation (8), and is mostpreferably narrowed beyond the width given in the equation above. Inaddition, the facet angles of the redirecting layer 224 are arranged tofocus the light output from different portions of the system-204 onto apreferred viewing zone. This figure also shows the micro-prismaticangle-transforming layer 274.

[0334] In FIG. 32C is shown a variation on the embodiment of FIG. 32B.In the system 204 an LCD layer arrangement 370 differs from the priorart LCD layer arrangement 310 illustrated in FIG. 30. In particular, aparallel light diffuser layer 372 (such as a holographic diffuser) isdisposed between the LCD layer 302 (layer 316 in FIG. 30) and the secondpolarization filter layer 322 (layer 314 in FIG. 30). This arrangementenables the second polarization filter layer 322 to reduce the glarewhich can otherwise be caused by ambient light being reflected by thediffuser layer 372. FIG. 32C further shows a light redirecting layer 374having curved refracting facets 376 which perform the same anglenarrowing function as the curved reflecting facets 362 shown in FIG.32B.

[0335] The following example illustrates a measurement system and methodfor various ones of the device 10.

EXAMPLE

[0336] The performance of the various devices 10 was quantified byintroducing a concept of useful system gain. The light outputdistribution from the devices 10 can be approximated by the sum of adiffuse Lambertian background and a one dimensionally collimated beamconsisting of a limited angle Lambertian distribution. In this model,the illuminance emitted into a limited angle (I_(imited)) from theluminaire device 10 can be expressed in terms of the peak luminance(L_(max)) of the toal distribution, fraction of the illuminance in thediffuse Lambertian background (α), and the width of the limited angleLambertian distribution specified by the limiting angles (θ⁺,θ⁻) in theform$I_{Limited} = {\frac{{\sin \left\lbrack \theta^{+} \right\rbrack} - {\sin \left\lbrack \theta^{-} \right\rbrack}}{1 + {\frac{1}{2}\frac{\alpha}{\left( {1 - \alpha} \right)}\left( {{\sin \left\lbrack \theta^{+} \right\rbrack} - {\sin \left\lbrack \theta^{-} \right\rbrack}} \right)}}L_{Max}}$

[0337] This is a useful quantity as it represents the total illuminancethat can be redistributed using various redirecting layers, such asangle transforming films and diffusers. Although the fraction of thetotal illuminance in the diffuse background can be quite large, themajority of the peak brightness is typically due to the limited anglelight emitted by the device 10 due to the much smaller solid anglecovered by the illuminance in the limited angular range case.

[0338] This idea was applied to a real device 10 by assuming that the+/−angles specified in the formula were the half-luminance pointsmeasured using a spot-photometer 498. For each set of measurements wemeasured the maximum brightness, and the angular location of thehalf-luminance points. The system 500 used to perform the measurementsis shown in FIGS. 61A and B. A few different diffusers were tried tovary location of the half-luminance points while maintaining the sameilluminance. Fitting this model to the data yielded a value for thefraction of power in the diffuse background. We found this value to be60.1% for the basic form of the device 10 used in our experimental work.FIG. 62 shows the measured data and fitted curves for a basic form ofthe device 10.

[0339] In the remainder of our work we quantified the performance of thedevice 10 by developing a set of gain factors based on the illuminanceestimate above. These gain factors were the total system gain(g_(total)), the brightness gain (g_(luminance)), and the gain due to anincrease in the solid angle of the illumination leaving the luminaire(g_(range)). These were given in terms of the measured luminance(L_(ref)), and an angular range factor (R_(u)) defined below. The highlyrestricted angle of illumination was only in a single direction of thedevice 10, so we used the one-dimensional formulas shown as the basis ofour analysis. In particular we defined: $\begin{matrix}{g_{total} = {g_{luminance}g_{range}}} \\{g_{luminance} = \frac{L_{sample}}{L_{ref}}} \\{g_{range} = \frac{R_{sample}}{R_{ref}}} \\{R_{u} = \frac{{\sin \left\lbrack \theta_{u}^{+} \right\rbrack} - {\sin \left\lbrack \theta_{u}^{-} \right\rbrack}}{1 + {\frac{1}{2}\frac{\alpha}{\left( {1 - \alpha} \right)}\left( {{\sin \left\lbrack \theta_{u}^{+} \right\rbrack} - {\sin \left\lbrack \theta_{u}^{-} \right\rbrack}} \right)}}}\end{matrix}$

[0340] Operationally, these measurements were made by dividing aluminaire device in two halves 502 and 504 (See FIG. 61B), both drivenby the same CCFT lamp, and with the sample light-pipe. For thosemeasurements that required coatings on or laminations to the light pipe,were laminated or coated only to half of the light-pipe. This method wasadopted for stability reasons, especially stability in the output of theCCFT lamp. We believe that the effect, if any, of this half-luminairemeasurement approach was to penalize our gain values. Since our goal wasto demonstrate attainable gains, such a potential penalty wasacceptable.

[0341] To obtain the final gain values reported in the tables, theobserved values were collected by the gains measured by making both thehalf-luminaires 502 and 504 of the same construction. This was tocorrect for a small side to side dependence that we observed. Thesecorrected gains (g_(corrected)) were calculated from gains of measuredsamples (g_(measured)) and calibration gains (g_(calibration)) measuredwith sides of the half-luminaire 502 in the reference configuration byjust

g_(corrected)=g_(measured)/g_(calibration)

[0342] Using this approach, a variety of luminaires were measured usinga Photo Research Pritchard Spot Photometer. To do the measurement, thedevice 10 was placed on a stand equipped with a rotation stage alignedso that during the rotation our measurement spot was stationary (seeFIG. 61A). Once the lamp in the luminaire at the center of each of thehalf-luminaires 502 and 504 (see FIG. 61B). For each measurement, alinear polarizer was used in front of the photometer 498 aligned to passthe maximum amount of light. For most of the measurements, thisdirection was horizontal or vertical with respect to the device 10 andinstrument, so the internal polarizers were used in the instrument forthese cases. For each of these halves, found the maximum brightness wasformed and then the angular locations of the half-brightness points byrotating the device 10 about a rotation axis.

[0343] While preferred embodiments of the inventions have been shown anddescribed, it will be clear to those skilled in the art that variouschanges and modifications can be made without departing from theinvention in its broader aspects as set forth in the claims providedhereinafter.

In the claims:
 1. An optical device for operating on light from a sourceand for selectively outputting light to a viewer, comprising: a baselayer having at least a first and second surface, said base layerfurther including a back surface spanning said first and secondsurfaces, and the light exiting said base layer when the light beingreflected therein decreases its angle relative to a normal to at leastone of said first and second surfaces at the point of light incidenceand achieves an angle of incidence less than a critical angle θ_(c)relative to the normal at the point of light incidence on said surfaces;first layer means disposed beyond at least one of said first and secondsurfaces relative to said base layer and for enabling light to enter andpass across said first layer means after output from said base layerwhen the light in said base layer achieves the angle of incidence lessthan the critical angle θ_(c) characteristic of an interface betweensaid base layer and said first layer; second layer means for preferablyoutputting light of a first polarization state compared to a secondpolarization state, said second layer means disposed beyond at least oneof said first and second surfaces relative to said base layer and saidsecond layer means further enabling reflection of at least part of thelight having the second polarization state; light control layer meansfor at least one of redirecting and diffusing light output from saidfirst layer means, thereby providing light of controlled angulardistribution; and imaging layer means for forming an image from thelight of the first polarization state for display to the viewer.
 2. Theoptical device as defined in claim 1 wherein said light control layermeans for redirecting light comprises a faceted layer for controllingthe angular distribution of light output from said optical device. 3.The optical device as defined in claim 1 wherein said light controllayer means for diffusing light is disposed at least one of (a) betweensaid base layer and said imaging layer and (b) between the viewer andsaid imaging layer.
 4. The optical device as defined in claim 1 furtherincluding converting means for changing light of the second polarizationstate to the first polarization state.
 5. The optical device as definedin claim 4 wherein said converting means is disposed at least one of (a)between said imaging layer means and said base layer and (b) furtherfrom said second surface relative to said first surface with saidimaging layer means disposed further said first surface relative to saidsecond surface.
 6. The optical device as defined in claim 1 wherein saidbase layer comprises at least one of a wedge-shaped layer, a disk, anoblate shape, a parallelpiped and a cylinder.
 7. The optical device asdefined in claim 1 wherein said imaging layer means comprises at leastone of a transparent display, a holographic image, a liquid crystallayer and a CCD layer.
 8. The optical device as defined in claim 1further including antireflection layers to reduce scattering.
 9. Theoptical device as defined in claim 1 wherein said light control layermeans includes a faceted layer of variable facet angles.
 10. The opticaldevice as defined in claim 1 wherein said second layer means is selectedfrom the group consisting of an optical interference layer, a Brewsterstack, a combination of the interference coating and the Brewster stack,a roughened surface, specular reflection layer, a dichroic layer, and abirefringent layer.
 11. An optical device for operating on light from asource and for selectively outputting light to a viewer, comprising: abase layer having at least a first and a second surface, said base layerfurther including a back surface spanning said first and second surfacesand the light exiting said base layer when the light achieves an angleof incidence less than a critical angle θ_(c) relative to a normal atthe point of incidence on said second surface; first layer means atleast one of disposed beyond said first surface relative to said baselayer and beyond said second layer surface relative to said base layerand having an optical index allowing transmission of light received fromsaid base layer, the light being output from said base layer uponachieving the θ_(c) characteristic of the interface between said baseand said first layer means; second layer means for preferablytransmitting light of a first polarization state relative to a secondpolarization state and reflects at least a portion of the light ofsecond polarization state, said second layer means disposed at least oneof (a) further from said first surface than said first layer means; (b)nearer said first surface than said second surface and said first layermeans relative to said base layer; (c) nearer said second surface thansaid first surface but further from said base layer than said firstlayer means; and (d) nearer said second surface than said first layermeans; light redirecting means at least one of overlying and underlyingsaid first layer means for operating on the light reflected by saidsecond layer means and redirecting it back toward said second layermeans; third layer means for converting at least part of the light ofthe second polarization state to light of the first polarization state;and a display layer positioned to receive the light of firstpolarization state output from said third layer means.
 12. The opticaldevice as defined in claim 11 wherein said means for preferablytransmitting light is disposed at least one of (a) between said displaylayer and said base layer and (b) further from said base layer then saiddisplay layer.
 13. The optical device as defined in claim 11 whereinsaid third layer means for converting light is disposed at least one of(a) between said display layer and said base layer and (b) nearer saidsecond surface than said first surface with said display layer disposednearer said first surface than said second surface.
 14. The opticaldevice as defined in claim 11 wherein said third layer means forconverting comprises a matching layer providing a preferred polarizationstate for said display layer.
 15. The optical device as defined in claim11 wherein said light redirecting means comprises at least one of (a) areflective layer able to reflect light, (b) a transmissive layer able tomodify the angular distribution of light passing therethrough, and (c) afaceted layer having a variable facet angle.
 16. The optical device asdefined in claim 11 wherein said display layer comprises at least one of(a) a liquid crystal layer, (b) a transparent display, (c) a hologramimage embedded in a medium and (d) a CCD layer.
 17. The optical deviceas defined in claim 11 further including light diffuser means fordiffusing light output from said display layer and broadening the lightin a controlled angular range to provide light to the viewer over arange of viewing angle.
 18. The optical device as defined in claim 130wherein said base layer comprises at least one of a wedge-shaped layer,a disk, an oblate shape, a parallelpiped and a cylinder.
 19. An opticaldevice for operating on light from a source and for selectivelyoutputting light to a viewer, comprising: a base layer having a firstand a second surface, said base layer further including a back surfacespanning said first and second surfaces; means for incrementallychanging an angle of light propagation in said base layer of saidoptical device, the light achieving an angle of incidence less than acritical angle θ_(c) relative to a normal to at least one of said firstand second surfaces at the point of incidence, the light thereby exitingsaid base layer; layer means for receiving the light from said baselayer and preferably outputting light of a first polarization statecompared to a second polarization state, said layer means includingmeans for preferably passing said light of first polarization state andreflecting at least part of the light of second polarization state andsaid layer means further including converting means for changing saidlight of second polarization state to said light of first polarizationstate; and a liquid crystal display layer positioned to receive saidlight of first polarization state.
 20. The optical device as defined inclaim 19 wherein said means for incrementally changing light anglecomprises a changing index of refraction in said base layer.